[unisog] Email for life

Paul Russell prussell at nd.edu
Tue Mar 23 15:27:49 GMT 2004

Daniel Feenberg wrote:

> 1) Reject spam and virus traffic during the SMTP transaction, rather than
> discarding mail later, or (worse) generating DSN mail. This isn't an easy
> ability to find - Can-it is the only such package I am aware of for
> Sendmail. Spamassassin could be run within a milter to do this, if you
> have the skills.

Sendmail can be configured to reject, at the SMTP level, messages for recipient
addresses which cannot be resolved via LDAP lookups.

> 2) Reject mail to overquota mailboxes. Note that if you offer pop service,
> sendmail (strictly speaking, the sendmail local delivery agent mail.local)
> can't do this right, since once the mailbox is more than half full, pop
> can't make a working copy of mailbox without busting the quota, and
> therefore won't allow the user to process his mail (including deleting
> messages). 

This is dependent on the structure of the mailstore. If individual messages are
stored as discrete files, rather than appended to a monolithic mbox file, the
'more than half full' problem is easily addressable. Several mailstore products,
including some open source products, provide this capability.

> There is an "FSTAT" patch for sendmail that could probably be
> modified to make sendmail respect quotas in a practical way 

If the MX service and the mailstore reside on the same server, this might
be possible. If they reside on separate servers, the problem becomes more

> or procmail
> could be so programmed (but that wouldn't happen during the SMTP
> transaction, so you would be sending DSNs for overquota messages, many
> of which would be going to forged return addresses). Perhaps other MTAs
> are better at this.

Paul Russell
Senior Systems Administrator
University of Notre Dame

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