--- name: "dccifd" section: "8" platform: "linux" package: "dcc-client" version: "1.2.74-2" release: "Debian 3.1 (Sarge)" platforms: ["linux"] url: "https://new.carta.tech/dccifd" --- # dccifd(8) Distributed Checksum Clearinghouse Program Interface ## NAME **dccifd** – Distributed Checksum Clearinghouse Program Interface ## SYNOPSIS **dccifd** \[**-VdbxANQ**\] \[**-G** *on* \| *off* \| *noIP* \| *IPmask/xx*\] \[**-h** *homedir*\] \[**-p** */sock* \| *host,port,rhost/bits*\] \[**-o** */sock* \| *host,port*\]\ \[**-D** *local-domain*\] \[**-r** *rejection-msg*\] \[**-m** *map*\] \[**-w** *whiteclnt*\] \[**-U** *userdirs*\] \[**-a** *IGNORE\|REJECT*\]\[ **-t** *type,* \[*log-thold,*\] *rej-thold*\]\ \[ **-g** \[*not-*\] *type*\] \[**-S** *header*\] \[**-l** *logdir*\] \[**-R** *rundir*\] \[**-T** *tmpdir*\]\ \[**-j** *maxjobs*\] \[**-B** *dnsbl-option*\] \[**-L** *ltype,facility.level*\] ## DESCRIPTION **Dccifd** is a daemon intended to connect spam filters such as SpamAssasin and mail transfer agents (MTAs) other than sendmail to DCC servers. The MTA or filter **dccifd** which in turn reports related checksums to the nearest DCC server. DCCIFD then adds an *X-DCC* SMTP header line to the message. The MTA is told to reject the message if it is unsolicited bulk. **Dccifd** is similar to the DCC sendmail milter interface, dccm(8) and the DCC Procmail interface, [dccproc(8)](/dccproc/8.md). **dccifd** is more efficient than dccproc but not restricted to use with sendmail. All three send reports of checksums related to mail received by DCC clients and queries about the total number of reports of particular checksums. MTA programs generally use a simple ASCII protocol to send a mail message including its SMTP envelope to the daemon. **Dccifd** responds with an indication of whether the message is unsolicited bulk and an optional copy of the message with an *X-DCC* header added. The protocol is described below and in the *include/dccif.h* file in the DCC source. There is a sample C interface routine in the *dcclib/dccif.c* file in the DCC source and the *dcclib.a* library generated from the source. A *Perl* version of the interface routine is in *dccifd/dccif.pl*. Test or demonstration programs in the style of [dccproc(8)](/dccproc/8.md) that use those interface routines are in *dccifd/dccif-test*. A subset of ESMTP can be used instead of the ASCII protocol to connect **dccifd** to postfix as a "Before-Queue Content Filter." See the **-o** flag. Since the checksums of messages that are whitelisted locally by the **-w** *whiteclnt* file are not reported to the DCC server, **dccifd** knows nothing about the total recipient counts for their checksums and so cannot add *X-DCC* header lines to such messages. The list of servers that **dccifd** contacts is in a memory mapped file shared by local DCC clients. The file is maintained with [cdcc(8)](/cdcc/8.md). Turn on the daemon and put its parameters in the *dcc\_conf*. Start the daemon with the *start-dccifd* script. ### OPTIONS The following options are available: - **-V** displays the version of the DCC program interface. - **-d** enables debugging output from the DCC client library. Additional **-d** options increase the number of messages. A single **-d** causes aborted SMTP transactions to be logged. - **-b** causes the daemon to not detach itself from the controlling tty and put itself into the background. - **-x** causes the daemon to try "extra hard" to contact a DCC server. Since it is usually more important to deliver mail than to report its checksums, **dccifd** normally does not delay too long while trying to contact a DCC server. It also will not try again for several seconds after a failure. With **-x**, it will always try to contact the DCC server and it will tell the MTA to answer the DATA command with a 4yz temporary failure. - **-A** adds to existing X-DCC headers in the message instead of replacing existing headers of the brand of the current server. - **-N** neither adds, deletes, nor replaces existing X-DCC headers in the message. Each message is logged, rejected, and otherwise handled the same. - **-Q** only queries the DCC server about the checksums of messages instead of reporting and querying. This is useful when **dccifd** is used to filter mail that has already been reported to a DCC server by another DCC client. This can also be useful when applying a private white or black list to mail that has already been reported to a DCC server. No single mail message should be reported to a DCC server more than once per recipient, because each report will increase the apparent "bulkness" of the message. - **-G** *on* \| *off* \| *noIP* \| *IPmask/xx* controls *greylisting*. At least one working greylist server must be listed in the *map* file in the DCC home directory. If more than one is named, they must "flood" or change checksums and they must use the same **-G** parameters. See [dccd(8)](/dccd/8.md). Usually all DCC client processes of dccm or dccifd should use the same **-G** parameters. *IPmask/xx* and *noIP* remove part or all of the IP address from the greylist triple. The CIDR block size, *xx*, must be between 1 and 128. 96 is added to block sizes smaller than 33 to make them appropriate for the IPv6 addresses used by the DCC. *IPmask/96* differs from *noIP* because the former retains the IPv4 to IPv6 mapping prefix. - **-W** turns off DCC filtering by default to ease managing systems where only a minority of users want unsolicited bulk mail to be rejected. This is equivalent to a *option* *dcc-off* line in the main **-w** *whiteclnt* file. When DCC filtering is off, the DCC server is queried and the *X-DCC* header is added but the message is marked to be delivered regardless of target counts and thresholds. DCC filtering is enabled for a mailbox when **-W** is not used and there is no *option* *dcc-off* line in the main or per-user *whiteclnt* file or there is a *option* *dcc-on* pine in the per-user *whiteclnt* file for the mailbox. DCC filtering can also be enabled with an "OK2" entry for the fully qualified mailbox in the main or per-user *whiteclnt* file. Messages sent *only* to target addresses that are listed in the global or relevant per-user **-w** *whiteclnt* file with "OK" are not reported to the DCC server and so are not rejected and do not receive *X-DCC* headers. - **-h** *homedir* overrides the default DCC home directory, which is often /var/dcc. - **-p** */sock/name* \| *host,port,rhost/bits* overrides the default address at which programs contact **dccifd**. The default is a UNIX domain socket named dccifd in the DCC home directory. The second form specifies a local host name or IP address, a local TCP port number, and the host names or IP addresses of computers that can use **dccifd**. 127.0.0.1 or *localhost* are common choices for *host*. The string *@* specifies IN\_ADDRANY or all local IP addresses. 127.0.0.0/8 is a common choice for *rhost/bits*. - **-o** */sock* \| *host,port* enables SMTP proxy mode instead of the ASCII protocol and specifies the address of the SMTP server for which **dccifd** acts as SMTP client. When */sock* is */var/null*, **dccifd** acts as if there were downstream SMTP server that always answers "250 ok". The string *@* specifies the same IP address as the incoming TCP connection. See below concerning the subset of ESMTP used in this mode. - **-m** *map* specifies a name or path of the memory mapped parameter file instead of the default *map* in the DCC home directory. It should be created with the [cdcc(8)](/cdcc/8.md) command. - **-w** *whiteclnt* specifies an optional file containing SMTP client IP addresses, SMTP envelope values, and header values of mail that is not spam, does not need a X-DCC header, and whose checksums should not be reported to the DCC server. Local whitelist *env\_To* values are handy for whitelisting or exempting destination addresses such as Postmaster from filtering and for blacklisting or marking addresses that should never receive mail. Mail sent to blacklisted addresses or with other blacklisted values such as From or env\_From values is reported to the DCC server as spam or with target counts of millions. If the pathname *whiteclnt* is not absolute, it is relative to the DCC home directory. The format of the **dccifd** whiteclnt file is the same as the *whitelist* files used by [dbclean(8)](/dbclean/8.md) and the *whiteclnt* file used by [dccproc(8)](/dccproc/8.md). See [dcc(8)](/dcc/8.md) for a description of DCC white and blacklists. Because the contents of the *whiteclnt* file are used frequently, a companion file is automatically created and maintained. It has the same pathname but with an added suffix of *.dccw* and contains a memory mapped hash table of the main file. A local whitelist entry ("OK") or two or more semi-white listings ("OK2") for one of the message's checksums prevents all of the message's checksums from being reported to the DCC server and the addition of a *X-DCC* header line by **dccifd** (except for env\_To checksums or when **-W** is used). A local whitelist entry for a checksum also prevents rejecting the message based on DCC recipient counts as specified by **-t**. Otherwise, one or more checksums with blacklisting entries ("MANY") cause all of the message's checksums to be reported to the server with an addressee count of "MANY". If the message has a single recipient, an *env\_To* local *whiteclnt* entry of "OK" for the checksum of its recipient address acts like any other *whiteclnt* entry of "OK." When the SMTP message has more than one recipient, the effects can be complicated. When a message has several recipients with some but not all listed in the *whiteclnt* file, **dccifd** tries comply with the wishes of the users who want filtering as well as those who don't by silently not delivering the message to those who want filtering (i.e. are not whitelisted) and delivering the message to don't want filtering. Consider the **-W** option for implicitly or by default whitelisting *env\_to* values. - **-U** *userdirs* enables private whitelists and log files. Each target of a message can have a directory of log files named *userdirs/addr/log* where *addr* is the local user or mailbox name computed by the MTA. The name of each user's log directory must be *log*. If it is not absolute, *userdirs* is relative to the DCC home directory. The sub-directory prefixes for **-l** *logdir* are not honored. The directory containing the log files must be named *log* and it must be writable by the **dccifd** process. Each log directory must exist or logging for the corresponding is silently disabled. The files created in the log directory are owned by the UID of the **dccifd** process, but they have *group* and *other* read and write permissions copied from the corresponding *log* directory. To ensure the privacy of mail, it may be good to make the directories readable only by *owner* and *group*, and to use a cron script that changes the owner of each file to match the grandparent *addr* directory. There can also be a whitelist named *userdirs/addr/whiteclnt* for each address *addr.* The name of the file must be *whiteclnt*. Any checksum that is not white- or blacklisted by an individual addressee's whitelist is checked in the **-w** **-whiteclnt** list. A missing per-address *whiteclnt* file is the same as an empty file. Relative paths for whitelists included in per-address files are resolved in the DCC home directory. The *whiteclnt* files and the *addr* directories containing them must be writable by the **dccifd** process. - **-a** *IGNORE* \| *REJECT* specifies the action taken when **dccifd** is in proxy mode with **-o** and the DCC server counts or **-t** thresholds say that a message is unsolicited bulk. *IGNORE* causes the message to be unaffected except for adding the *X-DCC* header line to the message. This turns off DCC filtering. Spam can also be *REJECT*ed. The default is *REJECT*. With an action of *REJECT*, spam sent to both white-listed targets and non-white-listed targets is delivered to white-listed targets and if possible, silently discarded for non-white-listed targets. This is not possible if there are too many non-white-listed targets to be saved in a buffer of about 500 bytes. The effects of the **-w** *whiteclnt* are not affected by **-a**. - **-t** *type,* \[*log-thold,*\] *rej-thold* sets logging and "spam" thresholds for checksum *type*. The checksum types are *IP*, *env\_From*, *From*, *Message-ID*, *Received*, *Body*, *Fuz1*, and *Fuz2*. The string *ALL* sets thresholds for all types, but is unlikely to be useful except for setting logging thresholds. The string *CMN* specifies the commonly used checksums *Body*, *Fuz1*, and *Fuz2*. *Rej-thold* and *log-thold* must be numbers, the string *NEVER*, or the string *MANY* indicating millions of targets. Counts from the DCC server as large as the threshold for any single type are taken as sufficient evidence that the message should be logged or rejected. *Log-thold* is the threshold at which messages are logged. It can be handy to log messages at a lower threshold to find solicited bulk mail sources such as mailing lists. If no logging threshold is set, only rejected mail and messages with complicated combinations of white and blacklisting are logged. Messages that reach at least one of their rejection thresholds are logged regardless of logging thresholds. *Rej-thold* is the threshold at which messages are considered "bulk," and so should be rejected if not whitelisted. The checksums of locally whitelisted messages are not checked with the DCC server and so only the number of targets of the current instance of a whitelisted message are compared against the thresholds. The default is **-t** *ALL,NEVER*, so that nothing is rejected or logged. A common choice is **-t** *CMN,25,50* to reject mail with common bodies except as overridden by the whitelist of the DCC server and local **-g**, and **-w**. - **-g** \[*not-*\] *type* indicates that whitelisted, *OK* or *OK2*, counts from the DCC server for a type of checksum are to be believed. They should be ignored if prefixed with *not-*. *Type* is one of the same set of strings as for **-t**. Only *IP*, *env\_From*, and *From* are likely choices. By default all three are honored, and hence the need for *not-*. - **-S** *hdr* adds to the list of substitute or locally chosen headers that are checked with the **-w** *whiteclnt* file and sent to the DCC server. The checksum of the last header of type *hdr* found in the message is checked. *Hdr* can be *HELO* to specify the SMTP envelope HELO value. *Hdr* can also be *mail\_host* to specify the host name from the Mail\_from value in the SMTP envelope. As many as 6 different substitute headers can be specified, but only the checksum of the first of the 6 will be sent to the DCC server. - **-l** *logdir* specifies a directory in which files containing copies of messages processed by **dccifd** are kept. All messages logged are copied to the **-l** *logdir* directory. They can also be copied to per-user directories specified with **-U**. Information about other recipients of a message is deleted from the per-user copies. If *logdir* starts with *D?*, log files are put into subdirectories of the form *logdir/JJJ* where *JJJ* is the current julian day. *H?logdir* puts logs files into subdirectories of the form *logdir/JJJ/HH* where *HH* is the current hour. *M?logdir* puts log files into subdirectories of the form *logdir/JJJ/HH/MM* where *MM* is the current minute. See the FILES section below concerning the contents of the files. The directory is relative to the DCC home directory if it is not absolute - **-R** *rundir* specifies the "run" directory where the UNIX domain socket and file containing the daemon's process ID are stored. The default value is often /var/run/dcc. - **-T** *tmpdir* changes the default directory for temporary files from the default. The default is the directory specified with **-l** or the system default if there **-l** is not used. The system default is often */tmp*. - **-D** *local-domain* specifies a host name by which the system is known. There can be several **-D** settings. To find the per-user log directory and whitelist for each mail recipient, **dccifd** must know each recipient's user name. The default ASCII protocol includes an optional user name with each recipient SMTP address. When that user name is absent or when the subset of ESMTP enabled with **-o** is used, each mail address is checked against the list of **-D** *local-domains*. If there is at least one match, the part of the recipient address remaining after matching the longest *local-domain* is taken as the user name. The matching is anchored at the right or the end of the recipient address. It must start at a period (.) or at-sign (@) in the domain name part of the address. - **-r** *rejection-msg* specifies the rejection message for unsolicited bulk mail or for mail temporarily blocked by *greylisting* when **-G** is specified. The first *rejection-msg* replaces the default bulk mail rejection message, "5.7.1 550 mail %s from %s rejected by DCC" The second replaces "4.2.1 452 mail %s from %s greylist temporary embargoed". There can be zero, one, or two "%s" strings. The first is replaced an empty string and the second is replaced by the IP address of the SMTP client. A common alternate for the bulk mail rejection message is "4.7.1 451 Access denied by DCC" to tell the sender to continue trying. Use a 4yz response with caution, because it is likely to delay for days a delivery failure message for false positives. If the bulk mail rejection message does not start with a recognized error type and number, type 5.7.1 and 550 or 4.2.1 and 452 are used. - **-j** *maxjobs* limits the number of simultaneous requests that will be processed. The default value is the maximum number that seems to be possible given the number of open files, select() bit masks, and so forth that are available. - **-B** *dnsbl-option* enables DNS blacklist checks of the SMTP client IP address, SMTP envelope Mail\_From sender domain name, and of host names in URLs in the message body. Body URL blacklisting has far too many false positives to use on abuse mailboxes. It is less effective than greylisting with dccm(8) or [dccifd(8)](/dccifd/8.md) but can be useful in situations where greylisting cannot be used. *Dnsbl-option* is either of the form *set:option* or of the form *domain*\[*,IPaddr*\[*,bltype*\]\]. *Domain* is a DNS blacklist domain such as example.com that will be searched. *IPaddr* is the IP address in the DNS blacklist that indicates that the mail message is spam. 127.0.0.1 is assumed if *IPaddr* is absent. IPv6 addresses can be specified with the usual colon (:) notation. Names can be used instead of numeric addresses. The type of DNS blacklist is specified by *bltype* as *name*, *IPv4*, or *IPv6*. Given an envelope sender domain name or a domain name in a URL of spam.domain.org and a blacklist of type *name*, spam.domain.org.example.com will be tried. Blacklist types of *IPv4* and *IPv6* require that the domain name in a URL be resolved into an IPv4 or IPv6 address. The address is then written as a reversed string of decimal octets to check the DNS blacklist, as in 2.0.0.127.example.com, More than one blacklist can be specified. They are searched in order. All searching is stopped at the first positive result. Positive results are ignored after being logged unless an *option* *DNSBL-on* line appears in the global or per-user *whiteclnt* file. **-B** *set:debug* sends more messages about all DNS resolutions to the system log. **-B** *set:msg-secs=S* limits **dccifd** to *S* seconds total for checking all DNS blacklists. The default is 20. **-B** *set:URL-secs=S* limits **dccifd** to at most *S* seconds resolving and checking any single URL. The default is 5. Some spam contains dozens of URLs and that some "spamvertised" URLs contain host names that need minutes to resolve. Busy mail systems cannot afford to spend minutes checking each incoming mail message. In order to use typical single-threaded DNS resolver libraries, dccm(8) and [dccifd(8)](/dccifd/8.md) use fleets of helper processes. **-B** *set:no-envelope* says that SMTP client IP addresses and sender Mail\_From domain names should not be checked in the following blacklists. **-B** *set:envelope* restores the default for subsequently named blacklists. **-B** *set:no-body* says that URLs in the message body should not be checked in the in the following blacklists. **-B** *set:body* restores the default for later blacklists. **-B** *set:no-MX* says MX servers of sender Mail\_From domain names and host names in URLs should not be checked in the following blacklists. **-B** *set:MX* restores the default. - **-L** *ltype,facility.level* specifies how messages should be logged. *Ltype* must be *error* or *info* to indicate which of the two types of messages are being controlled. *Level* must be a [syslog(3)](/syslog/3.md) level among *EMERG*, *ALERT*, *CRIT*, *ERR*, *WARNING*, *NOTICE*, *INFO*, and *DEBUG*. *Facility* must be among *AUTH*, *AUTHPRIV*, *CRON*, *DAEMON*, *FTP*, *KERN*, *LPR*, *MAIL*, *NEWS*, *USER*, *UUCP*, and *LOCAL0* through *LOCAL7*. The default is equivalent to ``` -L info,MAIL.NOTICE -L error,MAIL.ERR ``` **dccifd** normally sends counts of mail rejected and so forth the system log at midnight. The SIGUSR1 signal sends an immediate report to the system log. The reports will be repeated every 24 hours at the same minute as the signal instead of at midnight. ### Protocol **Dccifd** uses a simple ASCII protocol to receive mail messages to be checked and to return results. For each message, the MTA must open a connection to the interface daemon, send options, envelope recipients, and the message, receive the results, and close the connection. Instead of the ASCII protocol, a subset of ESMTP is enabled by **-o**. Only the familiar HELO, EHLO, Mail, Rcpt, DATA, RSET, and QUIT commands and the Postfix extensions XFORWARD and XCLIENT are honored. Since SMTP has no provisions for user names, the protocol enabled by **-o** depends on a list of local domain names specified with **-D** to find per-user log directories and whitelist files. If neither XFORWARD nor XCLIENT are used, **dccifd** uses the IP address of the MTA and the value of the HELO command. In the ASCII protocol, each of the following lines are sent in order to **dccifd**. Each ends with a newline ('\\n') character. - options zero or more blank-separated strings among: - *spam* the message is already known to be spam - *body* return all of the headers with the added *X-DCC* header line and the body - *header* return the *X-DCC* header - *query* ask the DCC server about the message without reporting it as if **dccifd** were running with **-Q**. - *grey-query* only query the greylist server for this message. **-G** *on* must be in use. - *no-reject* suppress the overall, one character line 'R' result. This can be useful when using **dccifd** only for greylisting. - client IP address of the SMTP client in a "dotted" or "coloned" ASCII string and reverse-DNS host name. If the host name is present, it must follow a carriage return character ('\\r') after the IP address. The client IP address must be present and non-null if the host name is present. If the client IP address is absent, then the IP address and host name are taken from the first Received header if it has the standard "name (name \[IP address\])..." format. - HELO SMTP HELO value or nothing, followed by a newline character. - sender or SMTP *Mail* *From* command value - recipients or SMTP *Rcpt* *To* values followed by corresponding local user names, one pair to a line. Each optional local user name is separated from the corresponding recipient address by a carriage return ('\\r'). A local user name can be null if it is not known. Recipients that lack local user names will lack per-user log files and will not invoke a per-user whitelist. The last recipient-user name pair is followed by an empty line and the headers and body of the message. The end of the body of the mail message is signaled by the MTA half-closing the connection. See [shutdown(2)](/shutdown/2.md). **Dccifd** responds with three things. First is a one character line of the overall result advising the MTA to - A accept the message for all recipients and answer the SMTP DATA command with a 2yz result. - G answer with a 4yz result to embargo the message for greylisting. - R reject the message and answer the DATA command with a 5yz result. - S accept the message for some recipients and so answer the DATA command with a 2yz result. - T temporary failure by the DCC system and so answer with a 4yz result. Second is a line of 'A', 'G', and 'R' characters indicating that the message should be accepted and delivered or discarded for each corresponding recipient. Limitations in the SMTP protocol allows only a single result for the DATA command for all recipients that were not rejected before body of the message was offered with the DATA command. To accept the message for some recipients and reject it for others, the MTA must tell the SMTP client it is accepting the message for all recipients and then discard it for those that would reject it. Finally, if the *body* or *header* strings are in the first line of *options* sent by the MTA to the daemon, then the *X-DCC* header line or the entire body with the *X-DCC* header line follows. ## FILES - */var/dcc* is the DCC home directory in which other files are found. - *libexec/start-dccifd* is a script often used to the daemon. - *dcc/dcc\_conf* contains parameters used by the scripts to start DCC daemons and cron jobs. - *logdir* is an optional directory specified with **-l** and containing marked mail. Each file in the directory contains one message, at least one of whose checksums reached its **-t** thresholds or that is interesting for some other reason. Each file starts with lines containing the date when the message was received, the IP address of the SMTP client, and SMTP envelope values. Those lines are followed by the body of the SMTP message including its header as it was received. Only approximately the first 32 KBytes of the body are recorded unless modified by *./configure* *--with-max-log-size=xx* The checksums for the message follow the body. They are followed by lines indicate that one of the checksums is white- or blacklisted by the **-w** *whiteclnt* file. Each file ends with the *X-DCC* header line added to the message and the disposition of the message. - *map* is the memory mapped file of information concerning DCC servers in the DCC home directory. - *whiteclnt* contains the client whitelist in the format described in [dcc(8)](/dcc/8.md). - *whiteclnt.dccw* is a memory mapped hash table of the *whiteclnt* file. - *dccifd.pid* in the **-R** *rundir* directory contains daemon's process ID. ## SEE ALSO [cdcc(8)](/cdcc/8.md), [dbclean(8)](/dbclean/8.md), [dcc(8)](/dcc/8.md), [dccd(8)](/dccd/8.md), [dblist(8)](/dblist/8.md), dccm(8), [dccproc(8)](/dccproc/8.md), [dccsight(8)](/dccsight/8.md), ## HISTORY Implementation of **dccifd** was started at Rhyolite Software in 2002. This describes version 1.2.74. ## BUGS **dccifd** uses **-t** where [dccproc(8)](/dccproc/8.md) uses **-c**. Systems without [setrlimit(2)](/setrlimit/2.md) and [getrlimit(2)](/getrlimit/2.md) can have problems with the default limit on the number of simultaneous jobs, the value of **-j**. Every job requires four open files. These problems are usually seen with errors messages that say something like ``` dccifd[24448]: DCC: accept() returned invalid socket ``` A fix is to use a smaller value for **-j** or to allow **dccifd** to open more files.