[@netweb Keymaster 12 years, 4 months ago]

Thinking on this some more, as it is a client site I presume it has it’s own domain name.

Is the clients domain name being used for the notifications with 2.5.1?
eg noreply@example.com

As you pointed out above that both the site URL and home URL use www and your emails are showing using the Bluehost’s subdomain box557.bluehost.com so is your site and home URL’s http://www.box557.bluehost.com?

And for completeness did your last test use changeset r5409 and 2618.4.diff?