This seems more a network issue than a TB issue. Also, your phone may be part of the connections. Additionally, servers sometimes get overloaded, and that's a possibility. My suggestion is to - ensure recheck mail timing is not less than every 15 minutes - change connections (assuming they are the default 5) to something less.

If that works, incrementally change the numbers to receive satisfactory performance.

these solutions don't seem to work for me. I still have the problem. Both the ISP an email host say Thunderbird is the problem. Please help?

What you could do is download a trial version of Postbox, as it is very similar and has most of the look and feel of TB and see if it produces the same results. that would bring you closer to identifying the issue.

I downloaded PostBox and have also tried again with a new account on Thunderbird and on both occasions I have now received an error saying: 'Failed to find settings for your email account'. I know the setting are correct because i can connect via a different PC using a different email client like Mail, which comes free on many PCs.

The fact that Postbox also gives the same answer implies the settings may need adjustment. I noticed also that your initial problem was imap server connection and now it is different. Maybe if you post info on your email provider and settings, someone here on forum can give feedback.

Actually I have been talking with the mail host for ages, and to no avail. Anyway, not sure why things have changed but today I started getting mail again on my TB out of the blue. Thanks for your help