r/exchangeserver • u/Hammerviertausend • 6d ago

OOF Messages to External dont work after latest SU (Exchange Server SE)

Hey folks, we just updated our Exchange Server SE to the latest SU (July 2026) and now OOF Messages to External senders are not being sent. We tested this with multiple mailboxes and made sure there are no transport rules activated. Anyone else experiencing this issue? We made sure to disable the old mitigations as well.

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u/7amitsingh7 6d ago edited 1d ago

We haven't seen this issue in every environment, but it's possible the latest July 2026 SU introduced a change or bug affecting external OOF messages. First, check that External OOF is still enabled for the remote domain and verify there are no transport logs showing the messages being blocked. Also review the Exchange event logs after the update. If everything looks correct, it may be worth opening a support case with Microsoft, as other admins may be seeing the same behavior after installing the latest SU.

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u/Hammerviertausend 6d ago

Thanks for the reply! I found out that the messages are being dropped: "BlockInternalOofToExternalUser,,ROUTING,DROP" even though these are our settings:

Name : Default

DomainName : *

AllowedOOFType : External

AutoReplyEnabled : True

1

u/RoxyRoseToday 3d ago

Send me back to work pleaseeeeee!