Mail Server Help

We have a client - that maintains their mail server in a different country. We act as a "relay" or more precisely as a back-up for their primary mail server, that is to say, on the MX record, our mail server IP is listed.

The client has a dedicated mail server (running on Windows/Visnetic Mail Server) with us.

All email coming to the domain for this client (for example) abcd.com is accepted and then after a virus check, if forwarded to our client's email server (which is on a dedicated network, to which we VPN).

As NO users accounts have been defined on our mail server, any mail for the domain abcd.com is accepted. Therefore email addressed to stupid_***@abcd.com would be accepted.

Of late, it seems someone is trying to run through a pretty comprehensive spam test list off this domain, i.e. we have been getting emails coming in at the rate of about 18,000 per hour. Emails like coofsdvoisjf@abcd.com, julia@abcd.com,
billgates@abcd.com, etc. etc.

Needless to say, because we are a mere relay, we have to accept such emails and pass them onwards. How can we stop this barrage of emails? One idea is obviously to setup all the User accounts on our mail server so any email not addressed to a specific user is rejected.

Any other solutions and/or thoughts that may come to you mind, please share.

If your solution translates to setting up a new server with a different OS and SMTP Server, please do let us know.

Since there is NO spam filtering done on this - I was thinking of installing SpamAssassin - but my fear or doubt is - would it do any good, as we think most of the messages coming through are blank/empty.

 

 

 

 

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