This happens sometimes. The fact that it usually works indicates your settings are ok, but the message is probably true: network slowdown, conflicts, overload, whatever... gremlins. It happens to me sometimes, but eventually clears up. There is probably a more technical answer, and it may be that the email provider is having technical difficulties at the moment. My backup for the duration is to switch saving messages to local folders.

Hi David,

I am saving to Local folders. Service provider not the problem, as I receive mail on my tablet - just not on my desktop in Thunderbird.

I do not understand. Is your problem in receiving or in sending? Your post gave impression that you are sending mail and and a copy is not being stored on the server - presumably an IMAP account. Please share more info. Thanks.

As per my thread heading 'Not receiving mail' - as soon as the: Your message was sent but a copy was not placed in your sent folder (Sent) due to network or file access errors. You can retry or save the message locally to Local Folders/Sent... message started coming up when I send mail, incoming mail also stopped.

So it seems the problem is two-fold. I also just noticed that my normal 'Sent' folder is empty. All previous sent messages have disappeared.

So, after restarting, and again selecting saving to Local folders, the message has stopped coming up when I send mail. I am still not receiving mail though.

This appears to be related to the account itself. I suggest logging into the online account to see what is happening. That is, if new messages are there and sent messages are there. What messages do you receive when attempting to receive mail? Posting screenshots of your incoming server settings and your SMTP sever settings may be useful.