That sounds like an anti virus meddling in the download until it times out. Do you have anti virus software?

Hi Matt, thanks for your help. No, I have no antivirus on the Mac. Nothing has changed in the configuration of my system or the version of Thunderbird for a long time, but this has become a problem over the past month or so. Today it's evolved - I had the same problem on one account - repeatedly downloading the same email every time it looks for new mail, but only downloading that one, not the more recent ones. And now, I've deleted that email from the central server, but it's still being downloaded continuously...

Have a look on the server in the spam folder. Sometime repeated duplicate emails are downloaded because of a badly formatted email (usually spam) that causes the connection to drop. So every time you connect it starts again with the last known good email. I have seen folks here that get a number of emails over and over.

Another less common cause is the connection simply being lost while email is being fetched. this can be caused by busy networks (kids and streaming in my case) the connection just times out because of network contention.

I've emptied out the spam folders for each account on the server, as well as physically deleting the offending emails (which now appears not to be working...). I can find plenty of advice suggesting deleting popstate files etc, but since this is on a Mac, that doesn't appear to be any help. Connection here is slow (rural location) but no other drains on bandwith at the moment as I'm here on my own and this is the only machine connected. The other suggestion I've seen is to go to IMAP. I'm reluctant to do that - I need offline access to emails when I'm travelling as I'm often without internet access for days at a time but still need to access emails and attachments for reference, not just draw them down from the server as I'm looking at them.

OK, so now the offending email (which has downloaded with its 13.3mb attachment at least 100 times today) has been deleted from the server, but it's still downloading every time I try to fetch mails, and blocking everythying behind it. This is driving me up the wall...

Right, so I seem to have found a temporary work-round. I went to the account settings for the particular account that was giving trouble, and ticked the 'Fetch headers only' box. That allowed the email and the ones backed up behind it to arrive safely. Then I unchecked the box again, and it's not trying to repeatedly download a non-existant email any more. TIme will tell whether it's just going to do the same again with the next email with an attachment it doesn't like... Thanks again for your input Matt.

I suggest you compact your store. File > compact folders. There will be a lot of wasted space to be recovered if the same mail downloaded 100 times.

It is possible if the connection is slow that there is a limit to how large an email you can download as well. There are some hidden preferences that can be used to extend the time out period, but I do not know if they still work.

It's set to compact automatically, so that should be ok. And I've deleted all the duplicate emails. I do have a very large archive of emails (all in subfolders) which I should probably store outside of Thunderbird, but I do often need these for reference. I'm not sure abou the connection speed idea - it would surely happen on all accounts, but in fact it's only ever happened on two out of three accounts (and not my main one). I find it curious also that in the latest episode it continued to download and show the rogue email long after that email was deleted from the server. Which hints more at a feedback loop within TB itself. But at least I've found a way to break the loop which doesn't involve deleting from the server. Yesterday my attempt to delete from the server caused problems for my wife (the problem was on her email address, which is a sub-account of mine) because she could then no longer access the email (which she needed) on her laptop at work. Thanks again.

What happens to you is "common" not to say normal.

Somehow either TB or your e-mail server "times out" before the e-mail transfer is completed and believes it was never really delivered, so next time your TB client connects, the Server tells it should download this message first (because it is first in the queue) and its all over again.

Deleting the message (FOR GOOD, even from Trash) should do the trick.

Obviously you don't want that. And you don't want that to happen AGAIN even if you choose to delete this one.

See if you can change the Timeout from either side and see if you can have a faster network to download this message in time. (is it taking too long to download just 13MB?)

Thanks for that. I'll investigate changing timeout settings (although I don't really know where to start looking...). Faster network isn't an option. I'm right out in the country, a long, long way from the exchange, and down the end of half a mile of copper cable that's been up on poles since the sixties and has been cut and spliced so many times it looks like macramé... On a really good, dry day I might get 0.6mbs download speed. Having said that, the speed's no worse than it's ever been, and I've never had this problem until a few weeks back.

I don't know how, if possible can you make changes or ask for changes to your provider.

OK, I'll investigate. If I find out anything useful I'll post back here in case anyone else has a similar problem.

If you don't need that e-mail message stored... just download the attachment from the Web interface and delete it for good.

If you need it, you can FORWARD yourself the message without the attachment. Delete the original copy and remove that message that is clogging your network.

Just a workaround

Yep, that's worked in the past. In this latest case though, even once I'd deleted the email from the web interface, TB was still repeatedly downloading it. How, I don't know. It wasn't until I switched to 'fetch headers only' that it managed to get out of its loop, get past that email and download the more recent ones.

Still no solution to this...