All of that migration happened in the cloud.

So are you saying all of your 20 years of email is now on the Gmail IMAP server? Do you see all your mail when logging into your Gmail account via webmail?

Now, in Thunderbird, I assume I need to change the IMAP Mail Server Name to the server address of my new GSuite account. Right?

Not necessarily. I'd advise against changing an existing account. Many people have wiped out their email archive that way. Even though that shouldn't happen in your case if the above is true, but you never know. I'd rather create a new account for the Gmail server. The flip side is, you'd need to download your entire archive once again, assuming you have turned on IMAP synchronization for the Gmail account. Also make sure you do have a backup of all your messages.

what will happen to the 25 gigabytes of locally stored email in Thunderbird when I change the IMAP Server Address?

If you do feel adventurous, I'd say give it a try and find out. But as said before, I wouldn't do it that way.

Thank you Christ1!

You wrote: >>So are you saying all of your 20 years of email is now on the Gmail IMAP server? >>Do you see all your mail when logging into your Gmail account via webmail?

Well, it turns out it is still in process of migrating. But, yes, I anticipate by tomorrow when the migration is complete, I will be able to see all 20 years of my email via Gmail in the browser. We'll see.

Regarding whether I should change the IMAP Server Address for my existing Thunderbird account, you wrote: >>I'd advise against changing an existing account. ... I'd rather create a new account for the Gmail server.

Okay that is a good idea. Thank you!

So... once I can see all my email on GSuite and once I have a backup of my current Thunderbird archive then I think the next step would be to delete the email account in question from Thunderbird, right? That will remove the 20 years of email from the Thunderbird archive, right? If so, it seems like I should then run File > Compact Folders, right?

If all of the above works then it seems like the final next step would be to set up my email account anew in Thunderbird and set the IMAP Server address to Gmail. Then Thunderbird should download the 20 years of email again, right?

Thank you again for your help! It is much appreciated. CS

I'd first create the new account, and only once everything is in place, delete the old one.

Many thanks Christ1.

You wrote: >>I'd first create the new account, and only once everything is in place, delete the old one.

Okay but question: can I create a new account using the exact same email address as an existing account. The only difference between the new account and the old account will be the IMAP Server Address. If Thunderbird will allow that then I will try it. Otherwise it seems like as long as all my mail is safely in the cloud with Gsuite I should be able to delete the old account from Thunderbird.

Thank you again for your help!!

can I create a new account using the exact same email address as an existing account. The only difference between the new account and the old account will be the IMAP Server Address.

Yes, you can. Just make sure to give the new account a unique name. There can't be two accounts with the same account name.

I'd at least make CERTAIN that the old and new accounts have different passwords and you make yourself enter the password for each one.

That way, you'll make sure you're doing what you want (migrate/delete/etc.) on the correct account and not blowup GMAIL.

Regards,

L