Skyy

This plugin allows you to banned certain username from making comment, particularly when you don’t want to ban 
ip addresses, but want to stop certain “notorious” misbehaving users.
If your blog requires user registration, you should really try the “members.0.1.1” wordpress plugin.

WP-Ban-User

Marian Kadanka

Override the default From: ‘WordPress <a href="mailto:wordpress@mydomain.com" rel="nofollow ugc">wordpress@mydomain.com</a>‘ name and email address.

Change From Email

Override the default From: 'WordPress ' name and email address.

WP-Ban-User vs Change From Email