Sending an email from one server to another using same domain name

Just rebuilt a companies website, updated their A records to point to it's new server location but kept their email function as was.

Sending from the server works fine, and they receive mail from elsewhere fine but now when trying to send forms as emails to their existing addresses they never arrive.

For example trying to send an email (more specifically a Drupal Webform) from domain.com from Server 1 to email@domain.com on Server 2.

I've tried adjusting the send add开发者_如何学运维ress from Server 1 which doesn't change anything. I think their IT person said something about receiving email at an exchange (Microsoft?) but I'm not savy this area at all.

Any ideas about this? I guess something is stopping it before it gets delivered (no spam) and the domains are conflicting, had a Google about but it's one of those where I'm not quite sure how to phrase the question. Thanks

SOLVED! In my CPanel I just needed to change my MX Entry to Remote Mail Server Exchanger