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.

My wife is having a similar problem. Here is more detail: With a "fresh" invocation of Thunderbird, all incoming messages are received, in two different email accounts. Outgoing messages can be sent. After a while (can be two days, can be a week or more), the error message shown above is received when sending an outgoing message. Once this error message happens, all incoming mail (for both email accounts) stops. If she then terminates Thunderbird, and restarts it, she will normally get an error message during the restart, which states that "Thunderbird is already running, but is not responding." If she accepts to terminate this non-responding process, then the next restart of Thunderbird is successful, and she can receive (and send) messages again. The workaround (as noted above) to save the sent message to a local folder allows the current outgoing message to be saved, and she can then copy the saved message to the proper "Sent" folder after she restarts Thunderbird. However, this is very annoying---having to save locally and then recopy---especially if there are several messages in progress when the failure occurs. In addition, it does not "solve" the problem; a restart is still necessary. A similar error message is presented sometimes, when Thunderbird is saving a draft message. It speaks of "a copy was not placed in your draft folder" (or something similar; I don't remember the exact details). When this error message appears, Thunderbird is in the same state as above: no incoming messages are received, and a Thunderbird restart is the only fix. Please note that this problem has been showing up for at least the last six to eight months. It seems to be getting more frequent, to the point where my wife now explicitly restarts Thunderbird every couple of days. Her environment: Windows 10 Enterprise; Dell tower; Thunderbird 128.4.2esr

I am also running Thunderbird on my laptop. I have six email accounts. I have never seen the above error message in relation to sending messages, although I have seen it concerning the saving of drafts. However, I have never seen it prevent the receipt of incoming messages, the way my wife has. My environment: Windows 10 enterprise; Lenovo laptop; Thunderbird 115.3.1

If there is a way to gather more extensive logs from my wife's computer, to aid in solving this problem, I will be happy to help. Please tell me what to do, or put me in contact with appropriate persons.

William, suggest you create a new posting https://support.mozilla.org/en-US/questions/new/thunderbird