Alias file sharing problem:
There is a bug in Mercury/32 versions prior to version 4.10 (unconfirmed if fixed in 4.10) that results in "Alias file sharing problem" error messages and the inability to send mail until Mercury/32 is restarted.
The problem arises from a virus that sends malformed eMail headers (basically a bug in the virus distribution code not properly implementing the mail specifications) that confuses Mercury/32 and causes it to leave a file handle open. Due to the way file handling works in Mercury/32, after several virus contacts, Mercury/32 runs out of file handles, making it unable to access the alias file (thus the Alias error message), which in turn disallows sending of mail (Error 421).
David Harris (author of Mercury/32) has been informed of this in January 2006. He indicated that version 4.10 rewrote the effected portions of the code and should eliminate the issue.
Release date of version 4.10 is unknown at this time.
Possible Workaround:
The virus works by using a specific email account name as part of the "HELO" string. So if the virus targets "username@email.com", it will send "HELO username" as the initial handshake message. You must kill it at this point because after sending two more lines, the Mercury/32 bug kicks in and a file handle is lost, eventually causing the bug detailed above.
So, simply add the following to "transflt.mer" using any text editor:
H, "*username*", BS, "554 Connection Rejected."
This line will reject anyone trying to use "username" as their identification. This shouldn't cause any mismatches as there shouldn't be a reason for a connecting mail client to use the destination account name as their own identification. Usually the virus works by a specific email address, so it's possible to block off all entry points by simply adding more lines with the account name targetted.
Note that you need to enable transaction-level expression filtering in the SMTP Server configuration page (under compliance).
Also, you may need to enable transaction logging (SMTP options) so you can track down which mail accounts were the target. Just search the content of the transaction logs for "PicSender_". This string is contained as part of each transaction and identifies the virus.