That really sounds like anti virus issues to me.

Try disabling email scanning and see how you go.

Matt, many thanks. I did just that and all of the mail downloaded almost instantaneously. the problem now of course is would I really want to run an e-mail program without scanning incoming messages? I use AVG 2014 and keep it updated. Something has changed to cause this, but what?

Two things.

1. AVG is preventing mail reception. Best ask AVG how to fix their A/V product.

1. Anti virus scanning of mail (particularly in Thunderbird) is not as important as most people think.

• Thunderbird has no scripts (so nothing can run when you open an email)
• Thunderbird has no or limited remote images (not that anyone can point be to malware that comes on an image file)
• Attachments are written to the temp folder before being opened. AVG and every other Anti virus program tell us it scans all files written to the hard disk. If their resident scanner is not good enough to catch malware in that file, is it good enough to protect you anyway?
• Bad links should be detected by the anti virus when they are opened in your browser. (If the anti virus can not do that then none of your browsing is protected. EMail is the least of your worries)

Matt, that all sounds very re-assuring. Thanks.

I have been in touch with AVG. They had no immediate answer but are investigating. Will post their response later.

I look forward to your solution from AVG. We catalog known issues here, https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues yours will be one of many unfortunately :)

AVG have not replied but late yesterday an update was downloaded. My PC is set to automatic updates for AVG and also Windows which also updated last night. Today, Thunderbird works well, collecting all new messages very quickly even with scanning enabled. If either of these updates were the solution to the problem I shall never know, but will leave it at that for now. Thanks for your help Matt