Adding a second domain into Active Directory for Office 365 logins

We have a hybrid Office 365 deployment with federated domains.

We have our school's domain and we have a second domain for school leavers (alumni) that they will keep when they leave school.

Both domains are federated and I can assign the primary email address from either domain however they still have to login with their school username.

I would like add the alumni domain into our active directory so that I can change their username from fred.bloggs@school to fred.bloggs@almuni

I want them to logon with their alumni email address/username rather than with their old school username as I can see it causing confusion going forward if they have different usernames and email addresses. Hope that makes sense.

I've been reseraching adding second domains and child domains but I'm not sure the best way to achieve this.

In a nutshell: I want to be able to choose either the school domain or the alumni domain under User Logon Name in the Account tab for that user's details in Active Directory.

What's the best way of achieveing this?

Thanks in advance.
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

David Johnson, CD, MVPOwnerCommented:
add the domain to office 365
o365 manage domains
itmtsnAuthor Commented:
The extra domain has already been added to Office 365.

What I want to do is change the username from user@school.domain to user@alumni.domain but because its federated it needs to be done in On-Premise Active Directory.

In Active directory I only get the option of the primary domain as user logon name so I'm wondering what's the best way to add the alumni domain in.

Vasil Michev (MVP)Commented:
Add additional UPN suffix via the AD Domains and Trusts console.
Have you tried adding a UPN suffix to your forest?
See this technet article for instructions to add the suffix:
you can then run through and change the default UPN for the affected users to use your new suffix.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Office 365

From novice to tech pro — start learning today.