Question : MDAEMON with SPAMSOAP SERVICE

I have an MDAEMON 7 Server behind a Netopia T1 firewall.  I also subscribe to a service called SPAMSOAP.  They are great as in we don't get many spams anymore!  For some reason though we are getting spam messages addressed to us from us!  I gues a spammer has found a way to send email to a registered user as that registered user.  I loked MDAEMON down in the security section and that has stopped.  SpamSoap reccomends that if your server is behind a firewall then you should lock down the server to only accept SMTP connections from their filter servers.

My question is:

How can I do what SPAMSOAP is suggesting?  I have used all my NAT translations allowed via the Netopia Router (for remote access and such!).  Can it be done in MDAEMON?  If it can will it block SMTP access from users who have BlackBerries and IPHONES?

Answer : MDAEMON with SPAMSOAP SERVICE

What you are seeing is known as Backscatter.  The latest version of Mdaemon has Backscatter protection built into it, but with older versions you can minimise the problem in various ways.  One is to add a header to all outgoing messages - say X-BACKSCATTER.  This is done using the Content Filter, which is under Security menu.  Now when you get a bounce-back you use another Content Filter rule to check for the presence of the X-BACKSCATTER header.  If it is there then the original message emanated from your domain.  If not then you can safely reject it.

Another thing you can do is to setup an SPF record, this doesn't prevent Backscatter, but at least if the recipient is geared up to check for SPF validity then they can work out whether there's any point in sending you an NDR.

http://www.openspf.org/