SMTP settings give 550 Unexpected response from SMTP server during handshake.

[Skyrider]

I've been trying to set up the SMTP settings within vBulletin email settings. Regardless of what settings/ports I use for non-encrypted, SSL or TSL, I always get:

PHP User Warning: 550 Unexpected response from SMTP server during handshake in ..../includes/class_mail.php on line 715

Now, I asked my mail provider to look into it further, and replied that the ACL triggered. And asked why the application is using HELO statement?

This is beyond my knowledge. Anyone happens to know?

rejected EHLO or HELO smtphosthere: Bad HELO - Host impersonating hostname

Regards,
Skyrider