Content filtering is done by programs like qmail-scanner or simscan. They gather the message and then pass it through various tests and/or external programs to verify that it's acceptable based on your sites policies.
How do I enable/disable a scanner?
Content scanners are enabled and disabled in one of two ways.
When using the latter method, you can even have mail from one IP range processed through Qmail-Scanner and mail from another through simscan. I suggest testing your scanner on a private or local IP before enabling it for all connections. When you do enable it, watch the logs for a bit and make sure it's doing what you expect it to. After editing tcp.smtp, run "qmail cdb" to rebuild the file.
Which scanner should I use?
Simscan is recommended and is the default.
Qmail-scanner is available if you choose to use it. It can filter based on external programs (ClamAV, SpamAssassin, etc) as well as things like attachment extensions, keywords, etc. It's very powerful, but has substantial resource requirements so use it with care. If you use qmail-scanner, it is activated at the system level and settings there apply to your entire mail server. If you must employ different policies for different [groups of] users, then you must do one of the following:
Simscan is small, fast, and solves most of the problems created by using qmail-scanner. It works with ClamAV, SpamAssassin, and Sophie. It has support for attachment extension blocking as well. You can set different options based on the email address or domain the message is destined for. It is the recommended tool.
Simscan can be configured independently for each domain. IE, you can enable spam filtering for one domain, but not others. You can exclude and include virus filtering on a per domain basis. The same goes for attachment blocking. It's very configurable.
Last modified on 4/28/05.