By default, gmail uses IMAP instead of POP3, although you can configure it to POP3. Google's AI says that gmail will be phasing out support for POP3, or at least requiring OAuth credentials to log in. I have one older non-gmail account that is POP3, but recently when I added a new gmail account I accepted the default IMAP protocol. The nice thing about IMAP is that you can access the account from any computer or your phone (there is now a Thunderbird app for Android - and probably IOS). I have not noticed any downside to IMAP and am planning to transition my old account over to IMAP. (You can force local storage of important messages by moving or copying them to "Local Folders") That said, to try to answer your question the way you asked it, have you looked under Tools: Account Settings: [your account]: Copies & Folders? Do you have the option for "When sending messages, automatically:" Place copy in "Sent" folder on [your email address] turned on?

Hi, thanks for answering. I do still have it set to POP3, and I have always had the default to put copies in the sent folder.

Any other ideas?

Also, if I want to change it to IMAP, how would I go about that? (If you want to point me to a clear description of this process written elsewhere that's fine with me.)

These instructions to changing to IMAP seem pretty clear to me.

https://support.mozilla.org/en-US/kb/switch-pop-imap-account#w_delete-your-pop-account

I have not done it yet, so I don't know if there's a catch. One thing I think may happen is you end up with two accounts that on the surface look the same, but one is inactive and one is active. If that's the case, you can rearrange the order of accounts in the left hand window to put the active one on top using Tools: account settings.

I don't have an answer as to why your sent mail is invisible.

Thanks. I'll give it a try. Meanwhile, anyone else have any ideas on the sent folder?

FYI, the sent folder it isn't invisible, it's there and it looks empty in Thunderbird. But the file in the appdata\profiles\ etc folder is quite large so I know the messages are there someplace, although the file size has barely changed since this problem occurred so I don't think recent messages are going there.

With pop, all folders are local. With imap, essentially all folders are remote.

So with pop, if messages are not being saved to Sent, then it is a local problem. First think to check is if the Sent folder settings are still correct. I just found that for my own pop account that the Sent folder is not even assigned as you can see in the screen shot - normally it points to the Sent folder for that "mail account in Thunderbird".

If that is correctly set but not working, one workaround that we see sometimes helps is pick "Other" and set the target folder per your wishes, which could even be the same folder that was assigned to "Sent Folder on:".

Please let us know what you learn.

Hi, thanks for answering. It did look correct ("sent on Jan") but I tried picking Other and forcing it to that same option and still messages aren't being saved.

FYI I have a few email addresses and had set my default "from" to a different address at some point. I tried forcing a message to be sent from the old one but still no save.

I've also tried compacting the Sent folder but since Thunderbird thinks it's empty nothing happens.

Have you tried the simple expedient of right clicking the folder and select properties and then the repair button. I am seeing more and more folks having issue with information stored locally because I think of their antivirus prodi8ucts scanning while Thunderbird is accessing the files. A repair (which is only an indexing process) may well just make everything appear. Likewise check you sent folder has column heading showing. Sometimes these get set to a null value and nothing appears because there are no heading for the information to display under.

To dispel any possible misunderstandings, I am not aware of any suggestion Google will phase out POP mail support. They have recently removed the setting in your google account to turn IMAP on and off and it is permanently enabled now. They have required oauth authentication on their mail account basically for a number of years. That was why Thunderbird automatically changed everyone's authentication to oauth2.0 with the release of version 91 in 2021 when Google first anounced they would be pulling less secure apps as an option.

See https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20

I did see the Google AI dribbling on about deprecation of less secure apps, like it was some ongoing project. They killed that option completely in January 2025 after years of steping lightly see https://support.google.com/accounts/answer/6010255?hl=en and the AI somehow managed to include POP in there because it was in my search term. It did not say anything technically incorrect, but as an information source on this occasion it leaves a lot to be desired. These guy did a much better job with the deprecating of less secure apps in September 2024. Something that involved just about all google sites and tools including mail. https://pipelinedigital.co.uk/blog/google-workspace-updates/gmail-to-end-support-for-less-secure-apps-what-you-need-to-know/

IMAP can simply be added to Thunderbird as a new account. I actually have the same gmail address added to my Thunderbird once as POP and again as IMAP as I occasionally want to check support issues on one protocol or the other.