I'm busy going through all of my domains on my server changing over from php mail() function to smtp authentication. All is going swimmingly apart from I've hit a snag with a couple of domains where they host their emails on their own internal server. An MX record on my web server is pointing their mail to their own server. This means I can't use my standard smtp authentication.

So basically 2 questions here:

1. should I get them to set up an email username and password on their own server and will that authenticate?


2. is their any other way of doing this that doesn't require my clients to get involved? The odd client might be stubborn and rather than help with setting up point 1 above, they may just move their hosting elsewhere.

Any help would be great