Procmail
| Procmail | |
|---|---|
| Basic data
|
|
| developer | Procmail Foundation |
| Publishing year | 7th December 1990 |
| Current version | 3.22 (September 10, 2001) |
| operating system | Linux , Unix |
| programming language | C. |
| category | Mail filter |
| License | GPL and AL |
| German speaking | No |
| www.procmail.org | |
Procmail is a Mail Delivery Agent (MDA) that is used to filter email messages on the server .
Usually Procmail is called by a Mail Transfer Agent (MTA) such as Sendmail or Postfix . Procmail can then pre-sort incoming e-mail messages into folders. E-mails can be filtered based on various properties, such as:
- Return address
- receiver
- Subject line
- Membership in a mailing list
- Content of the email
- Spam (in conjunction with spam detection programs such as SpamAssassin )
Procmail uses regular expressions for this purpose . Procmail also has the ability to call up external programs or to automatically reply to e-mails; popular features such as redirects , autoresponders or vacation schedules can be implemented.
To filter emails into existing mailboxes, Procmail provides the utility formail with.
example
The following example of a Procmail control file (usually .procmailrc ) scans incoming mail with SpamAssassin and then filters it.
SHELL=/bin/bash
MAILDIR=$HOME/mail
DEFAULT=$MAILDIR/inbox
LOCKFILE=$HOME/.lockmail
:0fw
| /usr/bin/spamassassin
:0H
* ^X-Spam-Level: \*\*\*\*\*\*\*\*\*\*
/dev/null
:0H:
* ^X-Spam-Status: Yes
./Spam
# Anything that has not been delivered by now will go to $DEFAULT
# using LOCKFILE=$DEFAULT$LOCKEXT
:0initiates a filter rule. The added fwrule of the first ensures that Procmail waits until the program is finished. The addition of Hthe following two rules ensures that only the headers of the email are searched. A final colon tells Procmail to use file locking. This is always necessary if it is not ensured that the rule can be executed several times in parallel. For example, if a mail is to be sorted into a certain mbox file, which would result in data loss due to simultaneous access .
To explain: First, the email is by means of a pipe to the program spamassassinsent and waiting until the program is finished. The now scanned mail runs through the next filter rules. SpamAssassin adds the header X-Spam-Statusto e-mails that have been viewed , which is Yes(for spam detected) or No(for messages not detected as spam) depending on the threshold set . SpamAssassin also adds a header consisting of *characters. The number of characters represents the rounded score (i.e. the probability that the message is spam) of the email. The default score by which a message is rated as spam is 5.
The example filters according to the number of characters. If Procmail finds ten or more *characters, the email is saved in the null device and thus discarded. If a message is generally recognized as spam, the message is saved in the Spam directory . All other e-mails are delivered in the normal inbox.
literature
- The Procmail Companion, Martin McCarthy , Addison-Wesley, p. 256, November 2001, ISBN 0201737906
- Procmail, Chris Lindsey , p. 325, April 2001, ISBN 1565925408
