I figured it out.
pop server: pop.something.net
smtp server: smtp.something.net
Frontgate is listening on 54110 and not 110
Avast MailScanner is listening on 110 (default)
E-mail client is configured for:
POP Server: pop3.frontgate.mail (127.0.0.1)
POP Port: 54110
SMTP Server: pop3.frontgate.mail (127.0.0.1)
Username: username/pop3.frontgate.mail:110
Avast MailScanner is configured for:
POP Server: pop.something.net
SMTP Server: smtp.something.net
I hope this information will help someone.