Hi Please explain exactly how you migrated your Thunderbird. Did you copy the entire Profile to the new machine? Are the versions of Thunderbird on both machines the same? Did you ensure that the new install of Thunderbird is connecting to the Profile that you copied over? It sounds as if your new install created a new Profile and is not using what you copied across.

Thanks for your response. I followed the instructions on the Mozilla website for migrating Thunderbird. I can't be sure that every single file is the same but the Worthwhile Messages files are in the same places and look the same on both computers. Thunderbird was already in use on the new computer. All the old emails came into that installation but Sent Messages didn't. Worthwhile Messages is on the new computer but I can't see it. I don't know how to control which profile I am using. Thanks for your help!

There are several methods for moving your profile, not sure which one you used. However if you had Thunderbird already in use, and merged the older messages with the newer ones, that's not a simple move. I am not sure how to help you further. You could try copying the mbox folders for Sent and Worthwhile into the Local Folders structure while Thunderbird is closed. Start Thunderbird and see if they appear in Local Folders. Then you should be able to move the messages to another location within Thunderbird if you need to. (You can confirm the location of Local Folders by looking in Account Settings -> [account name] -> Server Settings and see where it says "Local directory", browse to check or change the location of Local Folders.) It is possible you have ended up with more than one Profile folder - in %APPDATA%\Thunderbird\Profiles\ see if there are two or more folders with a random string folder name - one usually ends in .default, there may be more. It's not a problem to Thunderbird but having several old or empty Profiles might be confusing.

These are the instructions I used when I migrated Thunderbird: https://support.mozilla.org/en-US/questions/1349416#answer-1440652. The address book didn't come over either so I had to move that separately.

This is what I see under profiles. Not sure what it means.

I tried looking under Account settings and found Worthwhile Messages but it seemed to be empty.

At this point, would it be easier just to redo the migrating process?

Your link to the instructions seems to go to your own question. This question, not to instructions for migrating? Read the article "Where Thunderbird stores your messages and other user data" - it includes how to move your profile. Read all of it carefully so you understand how profiles work and where they should be located. After that, yes you may want to start again, copy the contents of your original profile from the older computer into the current active profile. Bear in mind that when you copy the whole contents of the original profile into the current profile, that will overwrite anything you changed since this started. Just make sure all your newer messages are still on the online server, then those newer messages should be unaffected and your older messages be restored. It is possible to direct Thunderbird to use a specific xxx.default profile - so if one of those three actually does contain all your older email with Worthwhile Messages in it, then you could follow the directions to have Thunderbird default to that profile from now on. See the article "Using multiple profiles" for how to change from one to another. Could be that is all you need to do. Note that if the folder you found under Account Settings was where Worthwhile Messages is - that means it is in Local Folders - a separate set of folders that is only on your computer. Be careful to identify Worthwhile Messages, the original version that is not empty, and make safe copies of that before you try moving things.

Thanks, Agnes!

Using Ubuntu 21.04 snap package install had to copy the contents of my TB 78 .thunderbird old profile (z9huh2kj.default-release) to the TB 91 .thunderbird install created profile (yfsn089s.default-release) for my emails to work. Notice I left the profile on 91 alone I just copied the contents of the profile folder 78 to 91 profile folder otherwise if you copy the profile folder itself it will not work, at least didn't for me. Calendars don't work however still trying to resolve that issue.