Depending on the SMTP server’s properties, sent messages can be copied to your sent messages IMAP folder by that server, after which they will be synchronized with your client (Thunderbird), or it requires you to set up that copy creation yourself in the client. Is there any chance the server changed that behavior?

This is assuming you had not set up Thunderbird to place a copy in the Sent folder yourself (in Account Settings > Copies & Folders). If you have, it should happen anyway and even twice if the server does the same. So indeed, given that all computers suffer the same issue, I would suspect the server to be at fault, changed behavior or requires you to set a (new?) option. If that cannot be fixed or handled, you need to set up the clients as above.

Tonnes said

Depending on the SMTP server’s properties, sent messages can be copied to your sent messages IMAP folder by that server, after which they will be synchronized with your client (Thunderbird), or it requires you to set up that copy creation yourself in the client. Is there any chance the server changed that behavior? This is assuming you had not set up Thunderbird to place a copy in the Sent folder yourself (in Account Settings > Copies & Folders). If you have, it should happen anyway and even twice if the server does the same. So indeed, given that all computers suffer the same issue, I would suspect the server to be at fault, changed behavior or requires you to set a (new?) option. If that cannot be fixed or handled, you need to set up the clients as above.

Thunderbird is set up to place a copy in the sent folder and our SMTP server is not. Using a different email client does exactly as you'd expect it to (places the copy in Sent on the SMTP and then the synched computers can download that copy). Thunderbird places the copy in the sent folder on the SMTP but refuses to download anything past 9/14. I doubt it's a server based issue since the behavior is exclusive to Thunderbird, but I will look into it.

Contacted our provider and they have said nothing has changed, still experiencing issue.

No offense to them, but helpdesks are often unaware of server changes or implementations and base their answers on number of similar compaints, and when Thunderbird is "officially not supported by them", you can expect any random answer.

Regardless, there are ways for you to check what goes wrong.

IBrewster said

Thunderbird is set up to place a copy in the sent folder and our SMTP server is not. Using a different email client does exactly as you'd expect it to (places the copy in Sent on the SMTP and then the synched computers can download that copy).

That seems contradictive and impossible if your SMPT server does not support performing the copy step, don’t you think? Unless you mean other clients do the copy step themselves too, after which they will be synchronized to the SMTP server and then back to other clients.

- Following that, are you actually sure Thunderbird uses the same SMTP server? - (Default action) Does the same thing happen in Safe Mode, i.e. could an add-on or theme cause this? - Does Thunderbird copy sent messages by other clients? - Do other clients copy sent messages by Thunderbird? - Check the Activity manager and Logs in Thunderbird. - Check the Copies & Folders section in Account Settings - instead of choosing "Sent folder on" you could select "Other:" and then point to the exact same folder. I do recall an issue in there years ago where that made a difference, so there could be a regression. - Check what happens if you set the folder specified in Copies & Folders to another folder. - Check your identities (even if you have one) - they have similar settings that override the general ones, including for what to do with the Sent copy, SMTP server, etc. - Check the subscriptions (right-click the account name in the left pane and choose Subscriptions) - is Sent checked? - You could enable Logging for IMAP or SMTP, but that would be the rough way.

I’m not aware of any bugs in TB release, nor any other changes/updates around Sept 14.

That seems contradictive and impossible if your SMPT server does not support performing the copy step, don’t you think? Unless you mean other clients do the copy step themselves too, after which they will be synchronized to the SMTP server and then back to other clients.

It supports performing the copy step, it is disabled as Thunderbird already creates a copy in the sent folder and we would be creating double copies. Each computer using Thunderbird has been set up to save copies to the sent folder on the SMTP account. These copies show up if viewing the inbox through the web based version of the mailbox or through other clients.

- Following that, are you actually sure Thunderbird uses the same SMTP server?

I'm not sure what you mean by this. The mail we send & receive is all coming through the SMTP server. Sent mail through Thunderbird shows up on the server, Thunderbird will just not show the newly sent mail that it stores on the server.

- (Default action) Does the same thing happen in Safe Mode, i.e. could an add-on or theme cause this?

There are no addons or themes installed on any of the clients. Do you mean system safe mode or does the program have a safe mode? I will attempt this.

- Does Thunderbird copy sent messages by other clients?

Thunderbird does not receive any sent messages no matter the origin of them.

- Do other clients copy sent messages by Thunderbird?

Other clients see mail sent by Thunderbird.

- Check the Activity manager and Logs in Thunderbird.

What would I be looking for here?

- Check the Copies & Folders section in Account Settings - instead of choosing "Sent folder on" you could select "Other:" and then point to the exact same folder. I do recall an issue in there years ago where that made a difference, so there could be a regression.

Doing this changed nothing, mail saved to server, Thunderbird did not display.

- Check what happens if you set the folder specified in Copies & Folders to another folder.

When a message is sent it appears in the new folder and is downloaded to Thunderbird as expected (This resolves the issue, though a second "sent" folder has to be used on the server rather than the original sent folder.)

- Check your identities (even if you have one) - they have similar settings that override the general ones, including for what to do with the Sent copy, SMTP server, etc.

The identity we are using matches the settings of the account. Both are set to copy the messages to the sent folder on the server.

- Check the subscriptions (right-click the account name in the left pane and choose Subscriptions) - is Sent checked?

Account is indeed subscribed to Sent.

One of the troubleshooting tips you gave soft fixed the issue but I'd like to get to the root of the problem if possible. Any tips on why it might be working with the newly created folder and not with the old?

IBrewster said

It supports performing the copy step, it is disabled as Thunderbird already creates a copy in the sent folder and we would be creating double copies. Each computer using Thunderbird has been set up to save copies to the sent folder on the SMTP account. These copies show up if viewing the inbox through the web based version of the mailbox or through other clients.

So you’re saying the SMTP server is disabled for generating the copies (how are you able to?), and hence all clients need the local step? Also, Thunderbird’s copy step is an addition for servers that don’t support it, so kind of the other way around, though using the local copy step everywhere could do no harm.

I'm not sure what you mean by this. The mail we send & receive is all coming through the SMTP server.

I just wondered if other clients using other software or even running Thunderbird use the same SMTP server as your machine - you wouldn’t be the first using another one that may not support the copy feature (when used that way.)

- Check the Activity manager and Logs in Thunderbird.

What would I be looking for here?

Good question. The Activity Manager should show the copy step when sending, I *think*, as the provider for my only IMAP-configured test account currently has issues (once again) so I can’t check. Filter logs and Junk logs probably don’t log anything important for this issue.

- Check what happens if you set the folder specified in Copies & Folders to another folder.

When a message is sent it appears in the new folder and is downloaded to Thunderbird as expected (This resolves the issue, though a second "sent" folder has to be used on the server rather than the original sent folder.)

I do understand the issue only occurs on your own machine, not for other Thunderbird clients, correct? In that case, it just looks like the issue is with the local Sent folder on your client only.

If things work when using another (new) folder for Sent, that shows there may be some corruption. This may be covered in this or this question.

One of the troubleshooting tips you gave soft fixed the issue but I'd like to get to the root of the problem if possible. Any tips on why it might be working with the newly created folder and not with the old?

I presume that is the last one?

Open your profile folder using Help > Troubleshooting Information, then click Open Folder. Close Thunderbird, navigate to the profile’s \ImapMail subfolder, then to the account name subfolder, and look for the Sent and Sent.msf files. Delete or move the Sent.msf file and restart Thunderbird and send a test mail.

If that does not help: in Thunderbird, move all messages in your Sent folder to another folder temporarily created in Thunderbird, then check the files in the profile as above when Thunderbird is closed - the Sent file should be empty - then just delete and recreate a Sent file sized 0 bytes and move the .msf once again.

I think the Sent file will even be recreated at launch and if not, you can create it from within Thunderbird where it should be gone, preferably in Offline mode, so enable that before closing it. Creating a Sent folder may not even be required as TB should sync with the server anyway. Then send a test message and see if it gets copied, and put back the moved messages when needed / not synchronized, or delete them.

Remember that all moves performed in TB’s online mode also occur on the server, hence the offline or file-level step. In short: basically you should be able to remove both files locally before starting Thunderbird, and everything should fix itself at launch and synchronization, as if you would set up the account as new.

Keep us posted.