Using Outlook 2010, three other accounts work fine; but one account has started showing an error (0x8004120A) with this message. I am able to ping the server and have adjusted the time before getting time outs. Seems to be on the receive side of the email stream. Account is on AOL mail. Webmail works fine.

Sort of at a loss on where to go next other than it does seem to be account specific.

Do you know if this is regular pop3 or pop over tls? Can you telnet to port 110 on the mail server and get a response. Are all the emails AOL? You really need to ditch pop if possible or use over tls at a minimum.

current connection is POP3; should I change over to IMAP then?

I think should understand why pop quit. Big deal is to get somewhere that the credentials are exchanged in a secure session. If all are connecting to the same mail server not sure the issue. But you can use putty or something similar to connect on port 110 and see if you see the pop initial message to ensure connectivity.

Outlook 2010, AOL, and POP. This thread is taking me back...

My recommendation is to use none of these, but alas