'Copying messages to Sent folder' doesn't complete

[#1]

Since last Friday messages I send through Thunderbird give the usual 'Copying messages to Sent folder' which, however, doesn't go away as it should. I have five such pop-ups showing now, one of them since Friday. If I select Cancel and Retry, I end up in the same situation. 

The messages are actually delivered. It's that it is not added to the Sent folder on my system and on webmail. Sending a messages through PN's webmail gets the message copied to the Sent folder, but then it doesn't show up in Thunderbird's Sent folder.  

So, it looks like Thunderbird can't use IMAP to copy a message to the Sent folder on the server.

My setup hasn't changed for ages. I have seen this behaviour before, but it is very rare one-offs and after a retry copying typically completes as normal. This time all outgoing PN messages are affected and never complete. 

[#2]

@glocal 

Using Thunderbird for two PN IMAP email accounts, one sends a copy of sent emails to the 'Sent' folder on the PN mail server (as you are trying to do), whilst for the other account a copy is sent to a local 'Sent Items' folder as I've set it up to do.

[#3]

@glocal 

Is it possible that when the outgoing message attempts to put a copy in the 'Sent' folder, that it is causing your account to exceed whatever quota Plusnet allows you to have, and therefore the copy fails to be written ?

In Thunderbird, you can check the quota usage, by <right-click> on your 'Inbox', then select [Properties] from the drop down menu, then in the "Folder Properties" pop-up windows, select the [Quota] tab, where you should see the usage something like this -

[#4]

I restarted the system and somehow the problem disappeared. It was false alarm I think. Strange it affected only one folder of one account. Thanks for the replies. 

[#5]

With Thunderbird, one needs to remember that it has its own LOCAL storage quotas which is not the same and the IMAP server's storage allowance.  See Thunderbird unable to save outgoing mails to sent folder | Howtoforge - Linux Howtos and Tutorials

[#6]

I believe this is to do with the 4GB max space that can be addressed in 32bit. I think users can make this hard limit irrelevant if they switch from mbox to maildir storage in TB. In any case, I was not anywhere near that limit. 

I find that sometimes PN's IMAP server is slow, and copying a sent message to the Sent folder on the server takes long, and instead of TB timing out and generating an error, it keeps waiting forever. In recent days this happens a lot more often, possibly because of the migration. 

[#7]

If you are discussing a large IMAP mailbox, then migration has no bearing on the experience.  None of the brands having a larger that 250MB mail store have yet been migrated.