Mail App crashes computer on start up

Mail App Crashes computer on Start up.

I have been having problems with the Mail app for some time. There has been an email in the outbox which i have repeatedly deleted and when I restart the email returns to my outbox. I cannot send nor delete the email. The app keeps giving a message that it is sending mail. I have to force quit the mail application so that I can use my computer. I would like to know how I can delete the mail app all together. I can use Outlook but this issue has been occurring since 24 December 2016. I have other user names in my computer but they don't have the email in the outbox and the computer doesn't crash on start up. I have scanned the email with a number of virus scanners and there appears to be nothing wrong with it so far as viruses or malware etc. My computer is not slow. I have 32gb of ram installed. My internet connection is no problem.

How do I delete the mail App!!!!