Hi David,
The F2S service appears to be hosted by TalkTalk, but I don't see email setting listed on their pages anymore -
TalkTalk Help
I recommend giving them a call and asking support for the current settings.
The server name is still inmail.f2s.com , regardless of if you are configuring SSL or not.
I did some checking and it appears that the mail server listed above does support both regular and secure POP3 & IMAP.
> telnet inmail.f2s.com. 110
Trying 85.119.249.98...
Connected to inmail.f2s.com..
Escape character is '^]'.
+OK <48925.1524055413@proxy005.apm-internet.net>
> telnet inmail.f2s.com. 995
Trying 85.119.249.66...
Connected to inmail.f2s.com..
Escape character is '^]'.
>telnet inmail.f2s.com. 143
Trying 85.119.249.98...
Connected to inmail.f2s.com..
Escape character is '^]'.
* OK APM IMAP Redirector ready.
> telnet inmail.f2s.com. 993
Trying 85.119.249.66...
Connected to inmail.f2s.com..
Escape character is '^]'.