Yes it's possible.   One way is to create a second domain name, then it's relatively trivial but you still need forward rules on both servers to send the messages to the correct host. And you have to configure the other host to accept the second domain name as an alias.   And a gateway rule for that second domain name.  You might also want a rewrite rule to change the wrong destination back to the right destination domain

You can just tell surgemail to send all bad addresses to the other server, which sounds like a simple solution, but if both servers do that then you get a loop

It's a very bad idea generally speaking.  The whole point of a domain name is to be a mechanism to get messages to the right server, and you are essentially saying 'lets not use the domain name' for what it's purpose is. 

ChrisP.

Hello,

If is possible to route messages if some users using other service like office 365 or gsuite

For example:

user1@domain.com and user2@domain.com using surgemail

user3@domain.com and user4@domain.com using office 365

I would like to know if there are some settings for forward or routing messages to user3 and user4 in office 365 server?

Thank you