popa3d patch for POP-before-SMTP and SMTP-after-POP

		    Garry Glendown / Dec. 12th 2000

On the 'net there are a couple of solutions to allow for POP-before-SMTP
authentication in order to allow for relaying of mails. Anyway, the 
solutions I found didn't really apeal to me, so I hacked popa3d a bit,
which we already used on one of our machines to serve mail to dialup
customers.

			     Prerequisites

This patch supplies data to sendmail to allow for certain IPs to use it
as a relaying host. In order to use with your sendmail installation, get
the popauth-hack (http://www.sendmail.org/~ca/email/rules/popauth.m4)
and install it by adding "HACK(`popauth')" to you .mc-file.

			       Installing

The patch - enabled through the POPB4SMTP-define in the Makefile -
accesses the file "/etc/mail/popauth.db" (create with "makemap hash
/etc/mail/popauth </dev/null") and adds the IP of the sucessfully
authenticated POP-user to it. Once the IP appears in the .db-file,
sendmail will allow the IP to relay mail from it.

Apart from the IP, which is added as LHS in the database, the patch adds
the timestamp of the authentication as RHS (which the sendmail-hack
ignores). This timestamp is then used to remove old IPs which are older
than VALIDTIME seconds (defined in the Makefile).

			       Disclaimer

This hack has been in production use for a week on our server and though
there are in average 30-60 POP3 logins per minute (going up to 2-3
requests per seconds during daytime), we have not had any problems.
Please note that I'm no expert at the Berkeley db library - I just
hacked up a version using the old db1 functions and it worked out.
There may be things to do better, but it seems to work fine for me. If
you have any suggestions, let me know ... I've tried to play it safe and
wrapped all db-access into a semaphore-protected block, hopefully
allowing for safe multiple execution ... also, I tried to make sure that
the string functions all check for the available array length.

If you have any suggestions, questions or feedback of any other kind
concerning this hack, don't bug the author of popa3d, but drop me a mail
at garry@glendown.de

G.Glendown / Dec 15th 2000

                                Testing

You can check the state by using the following command:
$ makemap -u hash popauth

On very low volume servers you may clean up the databse by setup a cron job:
cd /etc/mail && find popauth.db -mmin +6 -exec \
	makemap hash popauth.db <popauth ";"

Dirk Meyer / Jan 19th 2003