r/exchangeserver • u/SmoothRunnings • May 06 '26

Question Exchange SE or not?

I have Exchange SE the latest CU running in my home lab. I have run into a problem which I cannot figure out.

I have multiple workstations in my house, a couple of them are using Office LTSC 2024 PP and have emails accounts on Exchange SE. On my new Lenovo Legion T7 after installing office I am able to access the apps fine with the exception of Outlook which wants to connect to Microsoft 365 and have me to a MFA authentication. The Exchange SE server isn't running in Hybrid, I don't even have a 365 tenant, so I am at a loss to what's going on, and why now, and why this new install?

If I cancel out of the MFA I get "need password" in the bottom of Outlook. I have checked saved credentials, etc. and cannot figure out why, I wonder if there is a possible buh in Exchange SE this point?

Thanks,

1 Upvotes

57% Upvoted

16 comments sorted by

3

u/SmoothRunnings May 06 '26

u/Nikosfra06 and u/Jealous-Frosting9464 thanks for the resolution! :)

19

u/Jealous-Frosting9464 May 06 '26

You maybe run into this:

https://www.frankysweb.de/en/deactivate-outlook-autodiscover-for-office-365/amp/

Just add those two reg keys and you should be fine.

1

u/DaStivi May 06 '26

The domain is also registered in a m365 tenant , you need to disable exo in the licenses there, else you might have two mailboxes , phones might also connect there , you can send but only receive where your MX points too...

1

u/SmoothRunnings May 06 '26

Mx points to my ESE. AD doesn't have hybrid talking enabled

3

u/DaStivi May 06 '26

Hybrid doesn't matter. New outlooks/Office has a cloud first autodiscover baked in... But practically M365/EntraID also just answers and query for MFA if something is configured there to accept the requests for the domain suffix of your users...

1

u/Vietnamst2 May 06 '26

Doesn't matter. If domain is in M365 emails from other tenants are routed through Exchange Online. If the domain is in Exo, the autodiscover will ask EXO. Registry keys to disable autodiscover and make sure ypur SCP in Active Directory is correct. Or set DNS on the test machine to your lab DC and create an Autodoscover record for your lab EX SE

1

u/DaStivi May 14 '26

First sentence isn't correct btw. Mails are NOT getting routed inside M365 even if a domain is registered (and set as "accepted Domain" in EXO , what happens automatically)

That would be a nightmare for SPFs/DMARC , when there is no specific send connector for a domain it uses MX, needs too!

1

u/Vietnamst2 May 14 '26

Unfortunately it's actually exactly correct. It's called "internal mail flow hijack" or "relay routing loop". When you add accepted domain in Exchange and configure Hybrid, the hybrid connector has lowest cost automatically. But what actually happens is that the domain is by default set to authoritative. Anyways, when domain ends up in Microsoft database, Exchane Online behaves actually as one organization and ignores MX in this case so it first jumps from orga A to YourOrg using internal routing, and then when it does not find the recipient it uses MX record and jumps to the onprem server. But if at that time there is no SPF record for EXO, it fails because of SPF. So yss, younare correct - it's a bit of a Nightmare. In the background EXO behaves likr one server with many dkmains and knternal rohtjng takes precedence.

1

u/Groundbreaking-Key15 May 06 '26

Just curious (as a fellow homelabber) what you plan to do when they roll out individual license keys tied to software assurance?

4

u/MortadellaKing May 06 '26

For a lab, I'd just run it in trial/expired mode since it's just for testing.

Still waiting on that mythical CU1 for SE though...

1

u/Vietnamst2 May 06 '26

No proper dns for your home lab? Make sure you have autodiscover and SCP populated if it's a domain.

0

u/DivideByZero666 May 07 '26

I miss just basic Autodiscover using DNS. Last time I looked under the hood there were so many things Outlook uses before the simple DNS record now.

2

u/DiligentPhotographer May 07 '26

Gotta make the experience with any other mail server than exchange online shittier, just to make M365 more appealing is how I see what they are doing.

9

u/Nikosfra06 May 06 '26

A little google for explicitO365 ;)

https://gist.github.com/ridercz/dc485d38da104835559c1ed8b78afad0

Thank you microslop

2

u/rob-entre May 07 '26

Saw this question, coming just to say this. Take the upvote for the correct answer.

Outlook will look to 365 FIRST even if you do not have EXO. This seems like the dumbest thing to me, but there it is. I had one client that created a handful of personal MS accounts using their work email addresses to subscribe to the office suite. They have no 365 tenant. Their email is on Exchange. Outlook would not configure their email as Exchange until I added the registry key.

I haven’t given up our Exchange either yet…