Your faithful servant (OK, well, not really...),
Steve
Your faithful servant (OK, well, not really...),
Steve
If so, then the problem is with the destination mail domain. Either, your host has them blocked, or the destination domain has your hosting companies email servers blocked.
Either way, if you're on shared hosting, I check with them and have them confirm if mail is being rejected that belongs to you.
If you want to check if your server or their domain is on blacklists, use this:
http://mxtoolbox.com/blacklists.aspx
Just as an example, user's from freenet.de, never get my emails, cause freenet.de blocks my domain due to filters of their own...