Thunderbird is only an agent; the details relate to the email account itself. So, it may be helpful if you post specifics on the email account, such as screenshot of server settings and SMTP settings.

My service provider is Sasktel since I live in Saskatchewan, Canada of which is my internet and email service provider and due to this my server settings are

For incoming IMAP Server mail.sasktel.net Security Type SSL Port 993 and I have tried other ports settings as well that will work including the fact that tech service mentioned others that work.

Correct User name and email address including correct password

Outgoing Server SMPT Server smpt.sasktel.net Security Type TLS Port 587 (with other working Port numbers tried as well)

Require authentication to send emails also selected including normal password security selected as well.

Since Thunderbird accesses my email server it requires the correct Port settings, correct protocol and security settings and of course password for both incoming and outgoing.

Since this is all correct as per the customer technical support rep who also uses Tbird who while on the phone also gave me Port and Security settings. Besides this, they have a website telling what settings to use including myself referring to my Outlook Express in my Microsoft Office Pro for Port and server settings including on my cell, a Samsung Note 20 Ultra and when I change my password on the Sasktel server I have to go in on everything and replace my password. I'm even willing to uninstall Thunderbird and download a fresh copy and for this I would have to do a little research because even though I have been using Linux for a number of years, when it comes to using Terminal or Command Line Interface I have to find out what the proper commands are including proper procedure.

Should I consider uninstalling and then reinstalling my Thunderbird on my Ubuntu?

You'd be wasting your time. All your data such as messages, passwords and user preferences, and changes made while you use Thunderbird, are stored in a special folder called a profile. Your profile folder is stored in a separate place from the Thunderbird program, so that if something ever goes wrong with Thunderbird your information will still be there. It also means that you can uninstall Thunderbird and reinstall without losing your settings and data. https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data

Since Thunderbird accesses my email server it requires the correct Port settings, correct protocol and security settings and of course password for both incoming and outgoing.

Your server settings look good to me.

I think by mistake I deleted all of my emails BUT I have selected IMAP so my emails I want are still on my service providers server.

I have no idea how one can delete all emails by mistake. If you did this while Thunderbird was running, you possibly also deleted everything on the server. If you did this while Thunderbird was not running, your messages on the server should still be there. Having said that, using IMAP with all messages on the server is no replacement for a local backup.

I removed my account (I think) and go through the motions of reinstalling my account and get a pop-up indicating the server already exists which puzzles me.

I have no idea what you did, but you it may have messed up your profile. Create a new profile using profile manager. Start Thunderbird with the new profile also using profile manager, and re-create your account. Does it work then? https://support.mozilla.org/kb/using-multiple-profiles

Here is an update here to whoever considered my thought about the software being corrupt and removal was a waste of time! First of all being used on Ubuntu Linux I posted on the Ubuntu forum as well and they made similar suggestions. WHEN you have settings that worked before including the fact I have VPN and that raised suspicion so I disabled it even though THE SYSTEM WORKED BEFORE WITH VPN!. I contacted Sasktel BEFORE I removed it because I was working on a proper removal and FULL PURGE of this questionable software. I asked them about password security which raised questions in my mind because it is slightly different vs Outlook on my 2007 Office Pro. I experimented with NORMAL PASSWORD and AUTO DETECT which did not work and Sasktel tech support mentioned BOTH WILL WORK JUST FINE. ALL my settings were correct BUT it kept popping up the enter password window WITH CORRECT PASSWORD or REMEMBER PASSWORD SELECTED. My removal attempts would not remove it completely so this resulted in the reinstall attempt being again corrupted. IF YOUR SETTINGS ARE CORRECT and you get this repeated password rejection and IF you are using Linux and in my case UBUNTU 22.4.0 FOLLOW THESE STEPS! Backup your Thunderbird

https://www.technewstoday.com/how-to-backup-and-restore-thunderbird/

You need to make a backup and in my case I went to .home directory and at the advice of another Ubuntu member press control H and that will pop up hidden folders. This NOW MADE MY MOZILLA FOLDER APPEAR. This was before I used his above posted link and I went one step further and copied my entire mail. sasktel.net folder and anything else I thought would be important! As it turned out my steps were more thoral compared to the above link.

Next I entered Terminal and entered the following command and of course you need to enter your Linux password to authorize.

sudo apt autoremove --purge thunderbird

Your not done yet!! I kept installing with same password rejection fault! I went to .home directory and all of my earlier 2018 and later folders were still there

Go back again to .home directory: "Check in your home directory with {Ctrl + h} reveals hidden folders and in .mozilla folder look for thunderbird to see if anything remains." BEWARE of one fact about using control H with hidden folders!! Below my now visible Mozilla and Thunderbird folders appeared these folders but they were faint and lower contrast:

examples.desktop .bash_history .bash_logout .bashrc .ICEauthority .profile .sudo_as_admin_successful

These are likely important system files SO LEAVE THEM ALONE. ONLY DELETE ALL OF THUNDERBIRD

These were the other forum members instructions. Everything was back in there like before and total purge didn't removal all so the other member said "delete anything Thunderbird" which I now did.

Next I went back into Terminal and entered: sudo apt install thunderbird

It went through the motions of installation and I went into the Ubuntu Installed Software and it didn't appear but it was in the other applications directory so I sent it to my favorites on the desktop. Now when I opened it I went straight over to .home directory and checked and my earlier dated folders were now gone. I went into account settings and selected the correct IMAP settings including ports for incoming and outgoing mail and even selected Auto Detect and reentered my password selecting remember password and saved. NOW my Thunderbird is downloading all my emails but of course my contacts and address book is empty but I will recover them later on.

Yes this is an enormous amount of information BUT like I mentioned before

First check your port settings and ALL of mine including password were correct! I even contacted my service providers tech support for proper settings as well. I didn't stop there and went over to my online Sasktel webmail that is access to my account on the Sasktel server that can be accessed from any browser on any computer or smartphone. My email worked on my Samsung Note 20 It worked on Ourlook on Office 2007 Pro It worked on Sasktel webmail And of course it worked before on my Linux but several months earlier I changed password and this happened but removal of my email account and reinstalling it helped. Two months later this step didn't work and due to this glitchy behavior I suspected Thunderbird mail was corrupted!! Yes this time was another password reset but Thunderbird wouldn't accept the new password.

A great deal of information BUT I also didn't know the proper removal, the total purge and reinstalling procedures including using Terminal command procedures.

Christ1 Removal.of my account and reinstalling it would not work this time and is why with all my settings correct and verified correct is why I suspected corrupted software.

Congratulations. What you did was essentially create a new profile. This is exactly what I suggested to you earlier. As said before, re-installing the application was not necessary.

Congratulations. What you did was essentially not read my statement indicating Thunderbird WOULD NOT let me create a new profile🤔. Removing my ENTIRE account and reentering it WOULD NOT WORK including totally redoing my server settings, and this should not be required to have to do in the first place simply to replace a password???? 2 months ago I was forced to do this and that is the ONLY way I could change my password! This time, at the present time, it would not work and continued to reject a password that works on OTHER email clients including on the Sasktel server! Your statement will only lead others down the wrong path for a software installation that is defective due to corrupted software and this could have been due to an update gone wrong. You most certainly should not have to rip out your profile to change a password?????? How long does it take me to change a password (used on my Sasktel server) on my Outloook on Office 2007, or on my Samsung Note 20 Ultra, or other devices and even my account password on my Sasktel server? Step one) Enter settings, after opening the email client and locate server settings Step two) head over to password and back space or delete the characters and then reenter a new password and finally select save and it is done The same applies to ALL port and security settings on my Outlook and on my phone and even my Sasktel account using a web browser.

A friend of mine had his email account hacked and taken over by a flake commiting fraud by using his email account to send out emails to all of his contacts requesting the contact go out and purchase gift cards for a sick friend and I phoned him up and advised him his email account was hacked. For security reasons it is advised to change your password on a regular basis. My friends account was hacked 2 months ago prompting me to change my password as well and then the fun began and now repeated but to a worse degree presently. At least I was able to use Terminal and terminal commands and remove it along with looking in my Home directory and cleaning it out. A novice computer user unable to diagnose, remove, and reinstall this software would be unable and I know a number of people unable to do this.

Having to TOTALLY remove my account from the email client is totally unnecessary and IF this has to be done all the time on Thunderbird, it is a lousy design! It is a TOTALLY LOUSY DESIGN OR DEFECTIVE SOFTWARE? Again having to do all of this (removing my account as in the email address and my entire account worked 2 months ago but not at the current/present time! At the current time I had to TOTALLY PURGE EVERYTHING including going into my .home directory and use Control H to expose hidden folders and literally ferret out everything related to Thunderbird and reinstall and this clearly indicates something wrong within the folders that didn't purge.

During my search while attempting to find out what was wrong, I discovered another forum with another poster, posting identical symptoms as mine with all of his port settings correct like mine. His problem was also Thunderbird but also back in 2018. If you cannot replace a password with all port and server settings correct, including having to totally remove your account profile and 🙏, rip it out, purge it out and reinstall🤣. Next time I change my password and if this occurs I will do auto install and purge and look for another client. Thunderbird is the default email client provided and used on Ubuntu