Here's how to maintain an account in Thunderbird, but "disable" it so that it does not fetch messages when you click "Get Mail" (or when mail is retrieved at startup or periodically):

Tools >> Options >> Advanced >> Config Editor...

In the Filter bar, enter "server.server". Thunderbird apparently stores properties for each account under config items that have names like "server.server1", "server.server2", etc. So filtering on "server.server" will show you ALL of your accounts.

In the list, look for an item named something similar to this:
mail.server.serverX.name
...where X above is actually a number (1,2,3,...), depending on how many accounts you have.
...now browse through the list and look at the values of the items named "mail.server.serverX.name"...find the value name that corresponds to the email account you want to disable.
For example, if you discover that "mail.server.server6.name" has the email address for the account you want to disable, then...
...in the list, look for (or filter) "mail.server.server6.defer_get_new_mail" ... set this to false.

Thunderbird will no longer check that account for email.

This is obscure...but it looks like it works.

This article gives step by step instructions for how to import folders from another profile for a new user who has never installed an extension. It assumes you're using Windows but you should still be able to follow the instructions using a file manager on another operating system. The ImportExportTools extension can also be used to export folders.

Adds tools to import/export messages and folders (NextGen)

NEW 102 & 91 Compatible version . Linux & OSX PDF Export Support.

See Changes below

Finally, connect Thunderbird to your Exchange email account at your office.

You love Thunderbird. Your company uses Exchange.
Owl is the little bird that lets the two talk to each other.

See Move to a new PC or Moving your profile folder - Thunderbird if your profile is okay and you just want to move it. Most users who find this article should read one of those articles instead.

See Importing folders and Moving address books between profiles if you just want to move your folders and address books to a new profile that you create using the profile manager. If you do that Thunderbird will automatically run the new account wizard the first time you use the new profile. You will have to add your accounts again, customize your settings, and download/install any add-ons again. When Thunderbird needs a password it will prompt you for it. Enter it and check the checkbox to save the password. Unless you are using an add-on such as Lightning or Message Notes Plus you probably don't need to worry about moving anything else, and don't need to read the rest of this article.

Sometimes when you have problems with Thunderbird and can't figure out what's wrong, it's easier to create a new profile and transfer any data you want to save, rather than keep trying to fix your existing profile. In that case, read the rest of this article.

Thunderbird has a nasty habit of once in a great while forgetting about the existence of a profile if it uses the default name. When this occurs, you suddenly start up in the new account wizard and it looks like you lost everything. You haven't. It's just lost track of your profile, which is probably intact.

Another possibility is that your prefs.js file is empty or corrupt due to either Windows or Thunderbird crashing. Your prefs.js file has all of your account information and settings. In this case you haven't lost any of your mail or address books, but Thunderbird no longer knows how to fetch new mail or send messages, or display the folders in the folder pane. You'll need to recreate the accounts in Thunderbird unless you have a backup or unless it created a copy with a different name (for example, prefs-1.js).

If you have accidentally deleted one of your mail accounts by clicking on the "Remove Account" button in Thunderbird, this does not mean that your mail has actually been deleted from your computer. That mail should still exist in a child folder in the Mail folder in your profile folder. (This assumes that the account is not using the Global Inbox, in which case its mail would be stored in Local Folders.)

Once you've gone to your profile folder and verified that the mail for the deleted account still exists, do the following to get it back into Thunderbird. You may wish to make a temporary backup of your profile folder before proceeding.

ImportExportTools allows the user to export and import messages with more flexibility, with the following options:

Open your profile folder and see if you have a file named abook.mab.bak and another named history.mab.bak. Those are backups of your Personal and Collected addressbooks in the old .mab addressbook format (v78 does not use the mab format, but v68 does. This is one of the major changes introduced in v78). To restore those backups, simply rename them to their original name, e.g abook.mab and history.mab and restart Thunderbird.

You can run Thunderbird v68 with the --allow-downgrade commandline switch to downgrade your v78 profile for use with v68.

The Mailredirect extension for Mozilla Thunderbird and SeaMonkey adds the ability to redirect one or more email messages to one or more recipients.

The feature of email redirecting is also known as remailing or resending.
This extension is an answer for bug #12916.

Who wants this extension?

In office environment there is sometimes a need to forward email with original headers to somebody else. If Forward or Edit as new command is used, headers are very different comparing to original message (other From, Message-Id, Date fields). If you use the Mailredirect Extension headers are not changed, so the recipient of redirected mail has almost the original message. In practice all important headers in redirected message are identical to original one (From, CC, Message-Id, Date).

People who are "sorting" incoming email messages to their company are the first users who would like to use the Mailredirect Extension.
I think every experienced email user will appreciate the Mailredirect Extension.