Go into the site configuration tab in Site Admin. Create a new parameter with the name: Mail_Server_Host then give it a value of something like ''fake'' or ''no'' so that it doesn't try to use the mail host to send emails. Then click ok, once you have done this, now double click MAIL_SERVER_HOST value and verify the value is still what you put in, sometimes these values have a bad habit of defaulting back, if the value defaulted back change it again and click ok. Then try to send automail and see if the email goes through.

Sometimes even when mail feature is turned off the mail server value is not changed in the site params table in the DB, this method changes it so that QC does not have a correct email server to send mail from, if you ever want to use email again, just reconfigure the email settings in Site Admin.

NOTE: This will turn off all email functionality in QC.