SBS email stops downloading

[Pickle]

We are running, SBS 2003 Premium, letting it do what it wants, Everything.  DHCP, DNS,EXCHANGE POP, SQL, etc...   We have Mixed clients, MacOSX/98/XP pro, all set to POP3 and delete messages from server when read.  Fairly certian ISA is not the issue.   New installation  Avast SBS demo, attempting to convince the president to spend some money and get us off Symantec.

That being said
We first noticed the Macs stopped receiving email.  Exchange clients then started to time out, responding, some messages could not be retrieved from the server.  Using Eprompter mail previewer, downloading the message body would jam up.  IE: receiving 3 of 9.  Until it timed out also. 

Using Eprompter with the "Read mail headers only" selected, I could view the message headers, delete the unwanted mail, including "Avast Alerts", then the client could begin receiving email again.  It appears some email message bodies are being corrupted in some way as to block being read or deleted.

Now outbound emails are hanging up.  Not being delivered in the allocated time 24hrs.  Looks like I'm going to remove Avast SBS, so we can get back to work.  President is still waiting to be impressed.

[gemada]

We were experiencing the same problem with POP clients having the exact same issues. We discovered that when the Avast SMTP scanner on the server is adding a header saying that the message is clean, this header is somehow causing a corruption which leads to this problem. if you go into the Avast SMTP provider on your server, click on "customize", then click on "advanced" then remove the checkmark from "add information to message headers", this will solve your problem for all future emails (any pre-existing emails that are on the server waiting to popped will still have the corrupted header so you will need to forward them using another account or something to remove the problematic header). i am going to email Avast about this to see if they can replicate the problem. i have been able to replicate the problem by removing/adding the check mark as outlined above.