Hey Guys,

We have a new acquisition, and they want the cutover/MX record update to happen on a specific date. We already have mailboxes set up in our environment, since their current ones are going away. Can I set up an Accepted Domain and Email Address Policy for them beforehand (say a week in advance) without disrupting any mail flow, and then when the MX is updated we'll start to receive mail for them?

Thanks!

Yes, subject to mail flow to the other organization.  If you need that, make sure the accepted domain type is ExternalRelay, and make sure you have a send connector to route their mail to the appropriate host.