Domain Migration with O365 in the mix

[sgiovanni]

We are migrating from an old domain to a new one (pretty standard) but the kicker is the old domain is tied to Office365.  Does anyone have any experience/recommendations they can offer in regards to doing this in the least painful way?

So far we have ADMT up and running well and our test migrations have been successful, but what we are noticing is that the new domain-migrated account will only sync mail attributes once the old one is deleted, which plays havoc with our distribution groups, etc.

[#2 · Accepted solution]

It sounds like your source anchor may not have been configured to use ms-ds-consistencyguid as sourceanchor
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-design-concepts#using-ms...
OR
ADMT is migrating ms-ds-consistencyguid and other mail attributes (it does not by default, you must tell ADMT to move all attributes using a script)
OR
It could be your AAD Connect topology - you need to make sure that both forests are synced according to a supported multi-forest topology as documented here:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-topologies

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