Server disconnect on copying to sent items - using Thunderbird with imap

[#1]

This is not a new problem, but it seems to have got worse recently.

I use Thunderbird (60.0 - latest) for a total of four email accounts with Plusnet, plus some others with gmail. Initially I had it set for pop3, and all was well.

Then when I changed (all accounts) to imap I saw occasional 'server disconnected / timeout' messages on an email send, but generally on trying it again, it would all be fine. Ie, not right, but not a show stopper.

Now - last few weeks - I am finding that sometimes not only does it timeout on copying to sent items, but sometimes the sent email gets lost entirely. I am also not 100% convinced it always gets sent, though it may do.

Anecdotally, this seems to happen most if there is a reasonably long delay between starting Thunderbird and sending the email, say 5-10 minutes or more. If it is a question of: start Thunderbird, quick few words, send, it seldom fails - in fact I am not sure it ever does..

This only started to happen on switching to imap. I know sending has nothing really to do with imap / pop3, but that is what happened. Of course, with imap, after sending, there is some copying around of sent emails.

 There are various Thunderbird advanced settings for timeouts, none of which seem to have any effect. What is the case though is that the same Thunderbird also connects to some gmail accounts - also imap - and there is never a problem there. This only happens with the Plusnet accounts.

I also have Thunderbird on a Linux client, connecting to one of the same Plusnet accounts, and occasionally I've seen it happen on that as well.

On the other hand, with a mail client (gmail or bluemail) on Android connecting to the same Plusnet accounts, also imap, I do not see an issue.

It seems therefore that Thunderbird works fine with other email servers, and Plusnet works fine with other email clients. It is just the combination of Thunderbird, Plusnet and imap which doesn't.

I see on the internet I am not alone in this, but I do not see anyone posting a solution.

[#2]

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@nmw01223 wrote:

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Now - last few weeks - I am finding that sometimes not only does it timeout on copying to sent items, but sometimes the sent email gets lost entirely. I am also not 100% convinced it always gets sent, though it may do.

Anecdotally, this seems to happen most if there is a reasonably long delay between starting Thunderbird and sending the email, say 5-10 minutes or more. If it is a question of: start Thunderbird, quick few words, send, it seldom fails - in fact I am not sure it ever does..

...

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Thanks for posting details of your experience. Mine is similar though - with one exception when the network as a whole was in a "troubled" state - I'm not aware of any "sent" message not arriving at its destination. It's some weeks since I experienced a "copy to Sent folder" timeout, but then clicking Retry always worked. The actual 'Send' of course uses SMTP and 'copy to Sent' is IMAP. (When you used POP3, that copy didn't happen, Sent was a local folder.)

I think the anecdotal evidence you mentioned in the second paragraph of the quote has substance, those circumstances reflect my feelings too. I've had and continue to have behind the scenes discussions with a staff member about these issues. Reports are treated seriously though intermittent problems are always difficult to analyse. I don't think Thunderbird is blameless, for example bug report https://bugzilla.mozilla.org/show_bug.cgi?id=462156 started 10 years ago and still rumbles on today. That is for copying in the reverse direction, but the cause could be the same.

Have you noticed \answered flags not being set (or even set then unset again)? That is reflected in misbehaviour of the Replied To arrow in the message list

[#3]

You may well be right about sent emails not actually being lost, I am not sure. Since the SMTP bit will happen before the IMAP bit, it would seem likely.

The feeling I get about the fact that it appears to fail after no activity for several minutes - but not if sent immediately, is that maybe some connection when not being used goes into an idle state, or is disconnected. Perhaps there is a pool of connections at the server end. Then when you try to send the email, the time it all takes to wake up again is longer than some timeout at the Thunderbird end, so it says 'no server'.

I find a similar effect in a totally different area absolutely nothing to do with email or Plusnet - when I use remote desktop to a server. The first time I connect it often fails, but immediately try again and it works. Probably because whatever was asleep first time round and timed out, is awake and ready to go by the second attempt. Possible this is a similar type of effect.

However there are various timeouts you can set in Thunderbird under advanced settings, but none have had any useful effect for me. On the other hand, cannot find any description to say what any of them actually do.

Have you noticed \answered flags not being set (or even set then unset again)?

I haven't noticed anything about read / delivered flags as I seldom use them. On the reply icons in the message list, I do notice that one I did reply to (and now know did arrive), does not have a replied to icon, and that is one for which the sent reply definitely got lost.

[#4]

I can now confirm that the send itself sometimes fails, before getting to the point of copying to sent folders. So it is a general loss of connection issue.

I am seriously thinking of moving to a new email service. From other posts I can see I am not alone in this, but there does not seem to be any hope of its being fixed.

It is either that or change Thunderbird, however since I have so much stored in local folders, and Thunderbird works fine with other ISPs, it is probably best to find a different email service.