How does message ID being generated when sending out SMTP mail to Internet?

Hi all,

I wish to ask how is the messageID generated for the emails that are leaving the Domain to the Internet? I have encountered issue with emails that leaving the domain having their messageID carrign another domain.

For example, staff Andrew with email address andrew@abc.com sent a SMTP mail out of the Domain, it was shown that the messageID is 01234567890@xyz.com.

I can understand the left portion before the @ as it is the ID for this particular email. But in what situation can the right portion after @ be tagged with another domain name? And how does Domino pick up the information to tag it?

Any help will be greatly appreciated. Thank you.