mail opens slowly

So , is there any way that my mail application should work normally without deleting the complete mail account from system presences - internet accounts and then again configuring it .

Assuming you followed the instructions in the Discussion you recently replied to, that would be the next logical step. It's justified. Unless there is something unusual about the way you configured Mail to handle that account, no particular configuration is required.

Think of the way iOS does it: macOS Mail's "Rebuild" option doesn't exist, leaving no options other than temporarily disabling that Mail account. If that doesn't work the next step is to delete the problematic account and then add it again. Those two steps are described in detail here: Set up Mail with email accounts - Apple Support.

The problem could be related to Gmail (if that's what you use), or Malwarebytes. I don't use either one. Temporarily deleting one or both is the correct way to begin determining what's wrong.

You're welcome, and thanks for the kind words. Did you determine what fixed the problem?