--- name: "dcc-milter" section: "8" platform: "linux" package: "dcc-milter" version: "1.2.74-2" release: "Debian 3.1 (Sarge)" platforms: ["linux"] url: "https://new.carta.tech/dcc-milter" --- # dcc-milter(8) Distributed Checksum Clearinghouse Milter Interface ## NAME **dccm** – Distributed Checksum Clearinghouse Milter Interface ## SYNOPSIS **dccm** \[**-VdbxANQW**\] \[**-G** *on* \| *off* \| *noIP* \| *IPmask/xx*\] \[**-h** *homedir*\]\ \[**-p** *protocol:filename* \| *protocol:port@host*\] \[**-m** *map*\]\ \[**-w** *whiteclnt*\] \[**-U** *userdirs*\] \[**-a** *IGNORE* \| *REJECT* \| *DISCARD*\]\ \[ **-t** *type,* \[*log-thold,*\] *rej-thold*\]\[ **-g** \[*not-*\] *type*\] \[**-S** *header*\]\ \[**-l** *logdir*\] \[**-R** *rundir*\] \[**-r** *rejection-msg*\] \[**-j** *maxjobs*\] \[**-B** *dnsbl-option*\] \[**-L** *ltype,facility.level*\] ## DESCRIPTION **Dccm** is a daemon built with the sendmail milter interface intended to connect sendmail to DCC servers. When built with the milter filter machinery and configured to talk to **dccm** in the *sendmail.cf* file, sendmail passes all email to **dccm** which in turn reports related checksums to the nearest DCC server. **Dccm** then adds an *X-DCC* SMTP header line to the message. Sendmail is told to reject the message if it is unsolicited bulk mail. **dccm** sends reports of checksums related to mail received by DCC clients and queries about the total number of reports of particular checksums. A DCC server receives *no* mail, address, headers, or other information, but only cryptographically secure checksums of such information. A DCC server cannot determine the text or other information that corresponds to the checksums it receives. Its only acts as a clearinghouse of counts for checksums computed by clients. For complete privacy as far as the DCC is concerned, the checksums of purely internal mail or other mail that is known to not be unsolicited bulk can be listed in a whitelist to not be reported to the DCC server. Since the checksums of messages that are whitelisted locally by the **-w** *whiteclnt* file are not reported to the DCC server, **dccm** knows nothing about the total recipient counts for their checksums and so cannot add *X-DCC* header lines to such messages. Sendmail does not tell **dccm** about messages that are not received by sendmail via SMTP, including messages submitted locally and received via UUCP, and so they also do not receive *X-DCC* header lines. The list of servers that **dccm** contacts is in a memory mapped file shared by local DCC clients. The file is maintained with [cdcc(8)](/cdcc/8.md). Put parameters into the *dcc\_conf* file and start the daemon with the *start-dccm* script. When sendmail is not used, then **dccm** is not useful. [dccproc(8)](/dccproc/8.md) or [dccifd(8)](/dccifd/8.md) can often be used instead. ### OPTIONS The following options are available: - **-V** displays the version of the DCC Milter interface. - **-d** enables debugging output from the DCC client library. Additional **-d** options increase the number of messages. A single **-d**\ aborted SMTP transactions including those from some "dictionary attacks." - **-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, **dccm** normally does not delay too long while trying to contact a DCC server. It will not try again for several seconds after a failure. With **-x**, unresponsive DCC servers cause mail to be temporarily rejected with *4.7.1* *451* *DCC* *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 **dccm** 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 or discarded. This is equivalent to a *option* *dcc-off* line in the main **-w** *whiteclnt* file. When DCC filtering is off, mail is handled as if **-a** *IGNORE* were in use. The DCC server is queried and the *X-DCC* header is added but the message is 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 or discarded and do not receive *X-DCC* headers. - **-h** *homedir* overrides the default DCC home directory, which is often /var/dcc. - **-p** *protocol:filename* \| *protocol:port@host* specifies the protocol and address by which sendmail will contact **dccm**. The default is a UNIX domain socket in the "run" directory, often */var/run/dcc/dccm*. (See also **-R)** This protocol and address must match the value in *sendmail.cf*. This mechanism can be used to connect **dccm** on one computer to sendmail on another computer when a port and host name or IP address are used. - **-m** *map* specifies a name or path of the memory mapped parameter file instead of the default *map* file 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 spam or is not spam and does not need a *X-DCC* header, and whose checksums should not be reported to the DCC server. If the pathname *whiteclnt* is not absolute, it is relative to the DCC home directory. The format of the **dccm** 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 white-list entry ("OK") or two or more semi-white-listings ("OK2") for 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 **dccm** (except for env\_To checksums or when **-W** is used). A white-listing entry for a checksum also prevents rejecting or discarding the message based on DCC recipient counts as specified by **-a** and **-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". White-list *env\_To* values are handy for white-listing or exempting destination addresses such as Postmaster from filtering and for making "spam traps" of addresses that should never receive mail. First an entry for the official envelope *Rcpt To* value is sought. If that is not found, **dccm** looks for an entry for the sendmail "user" string. 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 message has a single recipient, an *env\_To* *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, **dccm** 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 white-listed) and delivering the message to don't want filtering. Consider **-W** or a *option* *dcc-off* line in whitelist files to turn off DCC filtering. - **-U** *userdirs* enables private whitelist and log files. Each target of a message can have a directory of log files named *usedirs/${dcc\_userdir}/log* where *${dcc\_userdir}* is the *sendmail.cf* macro described below. If *${dcc\_userdir}* is not set, *userdirs/${rcpt\_mailer}/${rcpt\_addr}/log* is used. If it is not absolute, *userdirs* is relative to the DCC home directory. The sub-directory prefixes for **-l** *logdir* are not honored. The directory containing the log files must be named *log* and it must be writable by the **dccm** process. Each log directory must exist or logging for the corresponding is silently disabled. The files created in the log directory are owned by the UID of the **dccm** process, but they have *group* and *other* read and write permissions copied from the corresponding *log* directory. To ensure the privacy of mail, it may be good to make the directories readable only by *owner* and *group*, and to use a cron script that changes the owner of each file to match the grandparent *addr* directory. There can also be *userdirs/${dcc\_userdir}/whiteclnt*, or if *${dcc\_userdir}* is not set, *userdirs/${rcpt\_mailer}/${rcpt\_addr}* per-user whitelist files. The name of each file must be *whiteclnt*. Every checksum including the *env\_to* and sendmail "user" values are looked for first in the userdirs/mailer/addr/whiteclnt and list then in the global **-w** *whiteclnt* list. A missing per-address *whiteclnt* file is the same as an empty file. Relative paths for whitelists included in per-address whiteclnt are resolved in the DCC home directory. The *whiteclnt* files and the *addr* directories containing them must be writable by the **dccm** process. The most likely value of *mailer* is *local*. Appropriate values for both *mailer* and *addr* can be seen by examining *env\_To* lines in **-l** *logdir* files. - **-a** *IGNORE* \| *REJECT* \| *DISCARD* specifies the action taken when DCC server counts or **-t** thresholds say that a message is unsolicited bulk. *IGNORE* causes the message to be unaffected except for adding the *X-DCC* header line to the message. This turns off DCC filtering. Spam can also be *REJECT*ed, or accepted and silently *DISCARD*ed without being delivered to local mailboxes. The default is *REJECT*. With an action of *REJECT* or *DISCARD*, spam sent to both white-listed targets and non-white-listed targets is delivered to white-listed targets and if possible, silently discarded for non-white-listed targets. This is not possible if there are too many non-white-listed targets to be saved in a buffer of about 500 bytes. Determinations that mail is or is not spam from sendmail via *${dcc\_isspam}* or *${dcc\_notspam}* macros override **-a**. The effects of the **-w** *whiteclnt* are also 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 or discard if not white-listed. Use **-a** *REJECT* or **-a** *Discard* to reject or discard bulk mail that is not white-listed. Use **-a** *IGNORE* *to* only add X-DCC headers with the "bulk" string. The checksums of locally white-listed messages are not checked with the DCC server and so only the number of targets of the current instance of a white-listed message are compared against the thresholds. The default is **-t** *ALL,NEVER*, so that nothing is discarded or logged. A common choice is **-t** *CMN,25,50* to reject or discard mail with common bodies except as overridden by the whitelist of the DCC server, the sendmail *${dcc\_isspam}* and *${dcc\_notspam}* macros, and **-g**, and **-w**. - **-g** \[*not-*\] *type* indicates that white-listed, *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 sendmail "resolved" 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 six will be sent to the DCC server. - **-l** *logdir* specifies a directory in which files containing copies of messages processed by **dccm** 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. - **-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 by the sendmail queue ID 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 from sendmail 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 **dccm** to *S* seconds total for checking all DNS blacklists. The default is 20. **-B** *set:URL-secs=S* limits **dccm** 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 ``` **dccm** 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. They will be repeated every 24 hours instead of at midnight. ## SENDMAIL MACROS Sendmail can affect **dccm** with the values of some *sendmail.cf* macros. These macro names must be added to the Milter.macros option statements in *sendmail.cf* as in the example "Feature" file dcc.m4. - *${dcc\_isspam}* causes a mail message to be reported to the DCC server as having been addressed to "MANY" recipients. The *${dcc\_isspam}* macro is ignored if the *${dcc\_notspam}* macro is set to a non-null string If the value of the *${dcc\_isspam}* is null, **dccm** uses SMTP rejection messages controlled by **-a** and **-r**. If the value of the *${dcc\_isspam}* macro starts with "DISCARD", the mail message is silently discarded as with **-a** *DISCARD.* This can be handy for keeping "spammers" from knowing they are sending to "spam traps." If value of the macro not null and does not start with "DISCARD", it is used as the SMTP error message given to the SMTP client trying to send the rejected message. The message starts with an optional SMTP error type and number followed by text. The **-a** option does not effect messages marked spam with *${dcc\_isspam}*. When the *${dcc\_isspam}* macro is set, the message is rejected or discarded despite local or DCC database white-list entries. The local white-list does control whether the message's checksums will be reported to the DCC server and an *X-DCC* SMTP header line will be added. - *${dcc\_notspam}* causes a message not be considered unsolicited bulk despite evidence to the contrary. It also prevents **dccm** from reporting the checksums of the message to the DCC server and from adding an *X-DCC* header line. When the macro is set by the *sendmail.cf* rules, *${dcc\_notspam}* macros overrides DCC threshlds that say the message should be rejected as well as the effects of the *${dcc\_isspam}* macro. - *${dcc\_mail\_host}* specifies the name of the SMTP client that is sending the message. This macro is usually the same as the *mail\_host* macro. They can differ when a sendmail "smart relay" is involved. The *${dcc\_mail\_host}* macro does not work if *FEATURE(delay\_checks)* is used. - *${dcc\_userdir}* is the per-user whitelist and log directory for a recipient. If the macro is not set in sendmail.cf, $&{rcpt\_mailer}/$&{rcpt\_addr} is assumed,but with the recipient address converted to lower case. Whatever value is used, the directory name after the last slash (/) character is converted to lower case. Any value containing the string "/../" is ignored. This macro also does not work if *FEATURE(delay\_checks)* is used. The following two lines in a sendmail mc file have the same effect as not defining the ${dcc\_userdir} macro, provided *FEATURE(dcc)* is also used and the sendmail *cf/feature* directory has a symbolic link to the *misc/dcc.m4* file. ``` SLocal_check_rcpt R$* $: $1 $(macro {dcc_userdir} $@ $&{rcpt_mailer}/$&{rcpt_addr} $)) ``` ## FILES - */var/dcc* is the DCC home directory in which other files are found. - *libexec/start-dccm* is a script often used to the daemon. - *dcc/dcc\_conf* contains parameters used by the scripts to start DCC daemons and cron jobs. - *logdir* is an optional directory specified with **-l** and containing marked mail. Each file in the directory contains one message, at least one of whose checksums reached its **-t** thresholds or that is interesting for some other reason. Each file starts with lines containing the date when the message was received, the IP address of the SMTP client, and SMTP envelope values. Those lines are followed by the body of the SMTP message including its header as it was received by sendmail and without any new or changed header lines. Only approximately the first 32 KBytes of the body are recorded unless modified by *./configure* *--with-max-log-size=xx* The checksums for the message follow the body. They are followed by lines indicating that the *${dcc\_isspam}* or *${dcc\_notspam}* *sendmail.cf* macros were set or 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 including SMTP status message if appropriate. - *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. - *dccm.pid* in the **-R** *rundir* directory contains daemon's process ID. The string “dccm” is replaced by the file name containing the daemon to facilitate running multiple daemons, probably connected to remote instances of sendmail using TCP/IP instead of a UNIX domain socket. See also **-R**. - */var/run/dcc/dccm* is the default UNIX domain socket used by the sendmail milter interface. See also **-R**. - *sendmail.cf* is the [sendmail(8)](/sendmail/8.md) control file. - *misc/dcc.m4* sendmail mc file that should have a symbolic link in the sendmail cf/feature directory so that *FEATURE(dcc)* can be used in a sendmail mc file. ## EXAMPLES **Dccm** should be started before sendmail with something like the script libexec/start-dccm. It looks for common DCC parameters in the *dcc\_conf* file in the DCC home directory. Those numbers should modified to fit local conditions. It might be wise to replace the "100" numbers with much larger values or with "MANY" until a few weeks of monitoring the log directory show that sources of mailing lists are in the server's whitelist file (see [dccd(8)](/dccd/8.md)) or the local *whiteclnt* file. It is usually necessary to regularly delete old log files with a script like libexec/cron-dccd. Sendmail must be built with the milter interface, such as by creating a *devtools/Site/site.config.m4* or similar file containing something like the following lines: ``` APPENDDEF(`conf_sendmail_ENVDEF', `-D_FFR_MILTER=1') APPENDDEF(`conf_libmilter_ENVDEF', `-D_FFR_MILTER=1') ``` Appropriate lines invoking the milter interface must be added to *sendmail.cf.* It should be sufficient to copy the dcc.m4 file to the sendmail 8.11 cf/feature directory and add the line ``` FEATURE(dcc) ``` to the local .mc file. ## 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), [dccifd(8)](/dccifd/8.md), [dccproc(8)](/dccproc/8.md), [dccsight(8)](/dccsight/8.md), [sendmail(8)](/sendmail/8.md). ## HISTORY Implementation of **dccm** was started at Rhyolite Software in 2000. This describes version 1.2.74. ## BUGS **dccm** uses **-t** where [dccproc(8)](/dccproc/8.md) uses **-c**. On many systems with sendmail 8.11.3 and preceding, a bug in the sendmail milter mechanism causes **dccm** to die with a core file when given a signal.