Automessage/Welcome Email

Hi

When using "Automessage' Plugin to create customer welcome email, this does not stop Wordpress from still sending its own which is driving me nuts. It says from Wordpress then I edited the pluggable file to say the name of my site instead BUT it still says the email sender is wordpress@mysite.com

Where can I disable this? or at least change the email sender to something different (really just want to get rid of it since im using automessage to do this) Thanks

Mike