Quote Originally Posted by curbsidestudiosNET View Post
521 Error - Blocked for abuse. Contact [email protected].
It's telling you that the server you're sending the emails from has been blacklisted due to abuse, probably abuse from spammers.

You should ask your hosting company to get your server off the blacklists.
And you'll probably have better success if you change your store to use SMTPAUTH instead of PHP as the email transport method ... you'll have to fill in all the SMTP settings on that screen too.

ref: http://www.zen-cart.com/wiki/index.p...Email_Problems
http://www.zen-cart.com/wiki/index.p...Of_Lost_Emails