how to reset thunderbird

[Camilia]

I need to reset Thunderbird in ubuntu 16.04. For email I try to add gives me memo that it already exist even though not on the list of incoming mail.

I tried removing it.

[kc1di]

I'm not sure what you mean by reset if you want to remove a server then you can do that by going to edit and Account settings and remove the account you no longer want
if you want to reset the whole program and start new with no accounts you can go to you /home folder or partition and set your file manager to show hidden files and delete the file .thunderbird. and when you restart thunderbird it will ask for you to create a new e-mail account (warning though if you delete the file you will loose all the e-mails you've already saved.) good Luck.

[Camilia]

That should work. For problem is that when i tried to add an email address got message email address already existed. Messages from Comcast should stay on their server?

[kc1di]

The default in Thunderbird is to leave them on the server I believe.
Are you using IMAP or Pop signin? IMAP leaves them there and just syncs your e-mail client to that.
Pop has a setting under edit>account settings>server settings just make use the box is checked that says leave on server.