[cobalt-users] MX problem ?

[support <mi@xxxxxxxxxxx>]

We have a user who occasionally uses mail2web.com to send/receive 
mail. Mail2web seems to send mail out as user@xxxxxxxxxxxxxxxx When 
someone replies to that, sometimes - not all the time - the message 
bounces and a Local configuration error is reported:

553 mail.domain.com. config error: mail loops back to me (MX problem?)
554 <user@xxxxxxxxxxxxxxx>... Local configuration error


I have MX records pointing domain.com to mail.domain.com and also 
www.domain.com to mail.domain.com.

Do I need to add another one pointing mail.domain.com to mail.domain.com??

thanks as always in advance...