mailscanner only sees the envelope TO

[Matt Kettler]

At 08:30 AM 7/16/2003 -0700, Ken Anderson wrote:
>MailScanner only looks at the envelope TO address, so if your mail
>server allows messages to have 100 recipients, you have 99 users who
>can't control what they perceive to be their own email filtering. :-(
>
>What is the best way to handle this issue?
>
>So far, we've limited the MaxRecipients in sendmail.cf to 10.
>Users don't send mail out through our MailScanner boxes, so this works
>reasonably well, since less than 1% of incoming mail is actually
>addressed to more than 1 user.

Unfortunately, since there's only one message at the transport layer, only
one action can be taken. It's either whitelisted or not.

SpamAssassin (a tool used by MailScanner) suffers from the same basic issue
whenever it's called at the transport layer. It looks at the body "To:"
header (along with some others), and must whitelist if any of the addresses
are whitelist addresses.

It's unfortunately impossible to magically make one message into many at
the MTA layer.. It's an inherent drawback.

Of course, you can switch to using tools that scan at the point of delivery
instead of transport, however those wind up scanning a message once per
recipient, instead of once, which increases overhead. It's kind of a
trade-off between flexibility and efficiency.

(Those who call SA from the MDA can force per-user preference files by
using spamc -u with the name of the actual recipient.)