He said me this:

Confirm first ‘what type’ of ‘smtp authorisation’ each isp was using prior to installing Avast. Pegasus allows 3 possibilities:

  1. ‘pop before read’.
  2. ‘Force’ username and password.
  3. get username and password from pop settings. (not necessarily in this order).

Try using the same authorisation method after installing Avast, and
‘possibly’ a combination of 1 and 2 above (Force and Pop before read)

Make certain the the smtp server ‘security’ tab > username contains the correct information required for the isp/Avast, i.e., user.isp#smtp.server (dependent on isp requirements). Of course the normal localhost routing (127.0.0.1) needs to be entered for the pop and smtp names.

All the above assumes the each Pegasus ‘Identity’ has individual pop and smtp profiles (better than trying to use the same pop smtp profiles on multiple ‘Identities’).

Does this help?