Thanks Rolf.  I think I know what's happening here.  For the account in question, all mail is intentionally being forwarded from another server (I cannot easily change this).  So, the immediate connection to Mercury is not from a spammer's server but from this forwarding host.  I don't think that connection control is going to help me in this situation.

Unfortunately, I haven't yet found any of these recent spamming hosts blacklisted, when checking with whatismyipaddress com, so Mercury's blacklist feature is not going to help either.

Gordon 

I have set up Mercury S Connection Control to Refuse connections from certain IP address ranges.  What I have found is that an initial connection attempt is refused but, if a second attempt is made by the same source (typically 1 second later), the connection is made and data is passed.  I don't understand why this is happening.

I am currently still using Mercury 4.74 and will be installing 4.80 as soon as I can find the time.  I am wondering whether this has anything to do wit the problem.

Thank you

Gordon 

We refuse tons of connections based on connections control entries, the short-time blacklist and a blacklist in an event daemon but haven't seen anything like this happen. Anyway, try updating to v4.80 (which won't take long) and let us know if the problem is still there.