Unable to write email to mailbox

Were things working OK for a while until this cropped up? How long ago did it start?

This is a tough one because the error message could be a server response indicating problems there, or it could be Thunderbird reporting difficulty transactioning with the server, or it could be a problem with Thunderbird itself. They can all trigger similar error messages, and the messages can be misleading.

Please check out this article and see if you think any of it applies to you. I suspect item #7, a malformed message on the server that Thunderbird is having trouble downloading. The solution is to use the email provider's web mail interface to delete that one problem message.

https://kb.mozillazine.org/Unable_to_write_the_email_to_the_mailbox

And here's another person with a similar issue who fixed it in a similar way as I described:

https://support.mozilla.org/en-US/questions/1463022

Also, Avast isn't the only AV that can lock up a file. Microsoft Defender can potentially do it, too, You can test that by creating an exception for your INBOX folder or whole Profile folder, or by restarting Windows in Safe Mode with Networking, which will temporarily disable the AV for that session.

Thanks for th information, I will check it all out. I basicaly had a program I was installing on my laptop blow it up. It was an older program that I used to use on WIn 10....something about one or more of the drivers it tried to install caused my laptop to stop basically bluescreen. I had managed to get a backup of most of my personal stuff but was more than a month out of date on my emails. Anyway - I restored what I could, then reinstalled Thunderbird - all looked pretty good, but then I started getting that error message. After I sent the info to you guys, I went to gmail online and cleaned up all my old email....needed doing anyway, then started working on getting my laptop reconfigured and set up. I got your email, then fired up Thunderbird and it downloaded all my outstanding email (163 messages in the last two days) without any error at all. It now seems to be working just fine. I have no idea what was happening or why but it seems to have cleared up. Nonetheless I will be looking into what you sent me. Appreciate your help with this.

Subject: POP3 "Unable to write the email to the mailbox" error with successful message download

Environment:

Windows 11 Thunderbird ESR 153 POP3 Gmail account AVG AntiVirus Free

Symptoms:

Thunderbird reports:

"Unable to write the email to the mailbox..."

Error Console reports: Incorporate write FAILED NS_ERROR_OUT_OF_MEMORY pop3MessageWriteError Despite the error, some messages are successfully written to the Inbox.

Troubleshooting performed:

Compacted Inbox. Rebuilt popstate.dat. Created completely new Thunderbird profile. Reconfigured POP3 account. Disabled extensions. Verified disk space and file permissions.

Observation: The problem persisted across profiles.

Additional testing: Temporarily disabling AVG Email Shield allowed large batches of messages to download successfully without the mailbox error. Later, after successful downloads, the problem ceased even after Email Shield was re-enabled, suggesting either:

an interaction between Thunderbird and AVG during POP3 message incorporation, or a transient state that was cleared by successful processing.