Weird email issue with a form

I suspect this issue is to do with some weird DNS setting somewhere, rather than the functionality of the form itself, so I only ask out of interest in case its something someone might have come across before.

Basically I have a form, and in testing it works fine with my personal and work email address.

But when I changed it to the address for the live page, it doesn't work.

Which would make me think that the issue was with the email address.

Except that if I send a normal email to that email address, it does work.

Meaning, weirdly, that the issue does not appear to be with either the email address or the form, but rather something specific to the form using that particular email address.

The only thing common to email addresses not working with the form is that they are all on the same domain.

Any ideas? (although asking you guys is a long shot with this one!)