After some recent reports by users I have looked in to the effectiveness of spam filtering on catch-all accounts. Internal testing and discussion with the mail server developers has brought out the fact that spam filtering is not applied to catch-all accounts.

Well that is not completely accurate. I should say spam filtering is not applied to catch-all accounts where the mail is received indirectly. Where mail is sent directly to the catch-all account spam filtering is applied as normal.

Example

Catch-all account the domain aguk.net has the catch-all account mail@aguk.net and no other accounts. Emails sent to mail@aguk.net are taken through the spam filter process including black and white lists. Emails sent to user@aguk.net are received by mail@aguk.net but DO NOT go through the spam filtering process including taking no account of black and white lists.

Apparently the reason for this is becuase the mail is received by the SMTP engine and then forwarded internally to the catch-all mailbox. The internal forwarding does not go through the SMTP engine and therefore does not have spam filtering applied.

There is nothing I can do about this at present since the developers state this would require a complete rework of the SMTP process. I will keep campaigning to have this changed while I also investigate if there are any workarounds.