HP-UX Mailing Solutions White Paper

• “Procmail Support” (page 35)
• “SpamAssassin Support” (page 36)
Milters
With the growth in email volumes and the prevalence of threats like spam, viruses, and targeted
attacks (denial of service, directory attacks), Sendmail is enhanced to provide the mail filter
(milter) functionality.
The milter functionality is available in Sendmail 8.13.3 on all versions of the supported HP-UX
11i operating systems. Milter provides a set of APIs that can be used to write many filter programs
and provides the following features
• Safety and security
• Reliability
• Simplicity
• Better performance
The milter API enables third-party programs to access mail messages as they are being processed
by an MTA. Therefore, third-party programs can examine and modify the message content and
meta-information during the SMTP transaction. Any number of filters can be added or modified
independently without impacting other existing milters.
Section illustrates the communication channel between MTAs and filters.
Figure 21 Communication Channel Between MTAs and Filters
Filters run as separate processes, outside of the Sendmail address space. Filters provide the
following benefits:
• The filter need not run with superuser permissions, thereby avoiding a large family of
potential security problems.
• Failures in a particular filter does not affect the MTA or other filters.
• The filter has high performance because of the parallelism inherent in multiple processes.
Many milter tools are available in the opensource. For information on the opensource milter
organization:
https://www.milter.org/
HP-UX provides following milter tools in the HP-UX Internet Express suite:
• Clam-AV®
• Milter-Regex®
Configuring Sendmail with Milter on an HP–UX System
This section discusses the prerequisites and procedure to configure Sendmail with Milter on an
HP-UX system.
Anti-Spam and Anti-Virus Solutions in HP-UX Sendmail 25