You can do quite a lot of filtering at the sendmail (or equivalent) level. For instance, you can reject all mail from sources listed in RBLs, you can reject all mail with a MIME type of multipart/replace, text/html or application/*. (multipart/alternative and multipart/mixed are legitimate.) Actually, I find that with the RBL filtering in place I never actually reject on MIME type.
If you reject messages at this level,you will reduce the load on your server and filters, quite considerably.
As an example, here is my sendmail config. It needs the check_local and check_header 'hacks' from the sendmail website, and regex maps compiled into your sendmail binary.
divert(-1)
divert(0)dnl VERSIONID(`@(#)generic-linux.mc 8.3 (Berkeley) 3/23/96') OSTYPE(linux)dnl DOMAIN(generic)dnl define(`confTO_QUEUEWARN', `24h')dnl define(`confPRIVACY_FLAGS', `authwarnings,noexpn')dnl FEATURE(`access_db')dnl FEATURE(`dnsbl', `spews.relays.osirusoft.com')dnl FEATURE(`dnsbl', `spamhaus.relays.osirusoft.com', `Open spam relay - see http:// www.spamhaus.org')dnl FEATURE(dnsbl, `relays.mail-abuse.org', `Open spam relay - see http://work-rss.m ail-abuse.org/rss/')dnl
KContentType regex -a@MATCH text/html|multipart/replace HACK(`check_header', `Content-type', , `ContentType',,,,,0,1, `MIME messages not accepted')dnl HACK(`check_header_end')dnl
MAILER(local)dnl MAILER(smtp)dnl
On 10-Jan-2003 Robert Tillyard wrote:
Does anyone know of a reasonably priced anti-virus product for Linux? Ideally we would want incoming and outgoing mail scanned and if possible HTTP/FTP downloads.
This is for Red Hat 7.3 to protect PCs that will be using it as a mail/proxy server.
Regards, Rob.
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