I just started having this problem. The email gets sent fine. The Sending message popup window that says "Copying message to sent folder" stays there forever. It never writes the email to my sent folder. It started yesterday, January 15 about 6pm Central time.

I have no mail quota issues. I am using WIndows 7 on a PC.

Since about two weeks ago, when I send an e-mail, I get the error message "Cannot copy mail to sent. Retry?" If you hit Yes, this just keeps on repeating itself. If you hit Cancel twice, the message goes away, the e-mail is sent, but not copied to the Sent folder. This happens with most, but not quite all messages, which makes it more confusing... I use TB52.6.0, Windows 10, and pop-smtp, so no question of mail quotas on the server or anything. It's a gmx.ch account. Any ideas?

Hi! I have the same issue, especially as Nagres describes in his post. I have tried everything I found in other posts, without result (checking quota, setting manually sent folder, creating a new Sent folder, etc.) I am using accounts for Gmail and for local private servers (ie. not large companies), same results. The "funniest" thing is, that the issue is not common, I could not filter out when it comes up! I think the issue might relate to (just ideas!): a) language issues. My Windows10 is Hungarian, but Thunderbird is English. Maybe that's an issue? b) opening/sending e-mails on different clients (ie. on PC and on iPhone too). I mean I receive an e-mail, after replies it becomes a chain, and some items of this chain are created on phone vs on PC, finally several Sent folders are used, so that could generate the problem? c) new e-mails, Re: e-mails, or further elements of a chain.

I am affraid the issue might be generated even the combination of a), and/or b), and/or c)

I am working on test cases as this issue is there since about november, 2017 on my Windows, but is started on my Ubuntu17 also (English Ubuntu, English Thunderbird)!

So far, in my testing seem to be sure: if a new mail is created on a PC, than the issue does not come up!

Hi Pilu36, "great" that someone else has this problem too... my case is much simpler than yours. I only use TB on one device (Win10 Laptop), all e-mails are downloaded to this machine, nothing is stored on the server. The strange thing is that this problem doesn't happen with all e-mails I send. Some are copied to Sent Mail without problems, others aren't. I haven't been able to see a pattern. But I do get the feeling that it is connected to another difficulty, namely that TB sometimes can't delete e-mails. I've tried all the solutions recommended in this forum, but that hasn't helped. This problem as well happens only intermittently, e.g. I can delete 5 messages, then it stops working, after 3 minutes I can delete another 3 messages. Very strange!!

OK, just one more idea, call it d) from my series above: mobile internet is less constant than wire-based? I am on mobile internet here at home, where the PCs sit. Could it be, that connection breaks up for the server? This came to my mind as your Delete process is hectic also. Just to reassure you: the problem with Sent messages is hectic for me too!

I don't think that could be an issue, as TB isn't supposed to copy anything back to the server at all! The sent and trash folders in my webmail account are empty. Or do I understand that wrong...?

to be honest, I am also just a user, kind of guessing, I don't want to mislead you. I don't what's happening, when an e-mail is sent out by a e-mail client (ie. TB). So I think we have to wait somebody with the necessary knowledge to help us. Anyway, I will do a focused test for various scenarios, it just needs a bit of time.