I have Netscape 7.2 mail clients (WinXPSP2) and the latest Avast Internet Mail scanner 4.6-763 blocks access from the Netscape email client and my POP3 servers. Doesn’t even get as far as asking for a password - it rejects the connection immediately.
The ISP mail provider is earthlink. The POP3 server is pop.earthlink.net port 110.
When I terminate (but not pause, pause also blocks the connection the server) the resident internet mail scanner the connection goes through. When the scanner is running - AND WITH ANY SETTING, that is, any level of heuristics, then the connection to the POP3 server is rejected.
Earthlink recently switched to an authenticated SMTP (outbound) mail server. The default port is 25 but port 587 can also be used. On this machine I found that port 25 did not function so I switched to port 587. Outbound mail is authenticated with the normal email password.
Oddly - when the email resident scanner is running I can SEND email on port 587 while POP3 access is blocked.