This has happened before, and I found something to put it right but cannot find now what it was that I did before!
Emails had been working fine until, suddenly, the following appeared:
Header download for the 'Inbox' folder did not complete. Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'imap.aol.com', Server: 'imap.aol.com', Protocol: IMAP, Server Response: '', Port: 143, Secure(SSL): No, Error Number: 0x800CCC0F
It is something straightforward, I think.
Hope I am in the right place