LegacyExchange Annoyance
(Exchange Cross Forest Migration Woes)

The Begining

I’m my quest to completely rebuild my company domain from the ground up (new Domain Controllers (Server 2016 Core), SQL 2016, SharePoint 2016, Exchange 2016….You get the idea) I’ve had to face many interesting challenges (not all blogged about just yet, but if you follow my TechNet posts you’ll see I have plenty of content to write about moving forward if I don’t come across interesting new things, at this rate that seems unlikely… anyway) This time it was another interesting one.

The Weekend

After spending the entire weekend combing over every little detail of the migration (Mail relays, systems that use email, how they send email, the receive connectors they would need (Auth types, TLS sec, etc) I figured I had all my bases covered, and made the switch (all changes including expanding existing server configs to allow mail flow, not hinder any) so the last part of my switch was ensuring most servers/services were using a Fully Qualified Domain Name (FQDN) in their settings/configs for SMTP. So my cut over in this case was very simple change the A host record, and clear all systems DNS cache. To my amazement everything was still working (even ActiveSync cut over without a hiccup)…. Until… the next day…

The Next Day

Out of all things I didn’t anticipate internal email flow to break… I mean… there’s nothing different between Joe.blow@corp.ca and Joe.blow@corp.ca right??!?! Wrong! lol with Microsoft Exchange you are totally, and utterly wrong! First… Read this and read this to understand exactly what I mean. In short internal email likes to use it’s own special address… (give a dirty look)… called X.500 addresses (AKA The LegacyExchangeDN) bunch of garbage, muff cabbage BS…. So instead of everything resolving normally cause all new linked mailboxes had the proper SMTP address (So all other outbound/inbound flowed without issue), user wanting to reply to old emails, or creating new ones and having the TO field be auto populated, they would get a stupid NDR (AKA a bounce back telling them the email can’t be sent to the recipient) cause FFS it can’t just use the SMTP address NOOOOOOOO it uses the stupid Legacy X.500 Address… Gosh Darn *Mumbles* Exchange… in case you can’t tell I dispise email with a passion.

The Search

Anyway, I looked up what the possible solutions were, I wasn’t too happy. For now I was telling people to simply remove the old Auto Populate cache Outlook was using. As for existing Calendar events, turns our all resources fell under the exact same annoying problem, even though I created them all with the same alias’s it wasn’t good enough Exchange was seeing them via their old X.500 addresses (Since all old Calendar Items were imported from Backup), they had new X.500 addresses in the new Exchange Server. So I would have to tell people to remove those resources, and simply re-add them.

The Problem

There is however a problem with this, and that is if someone edits an existing Calendar event and changes the time, the room may already have been booked (the new room) so when the user editing the old re-occurring event goes to re-add the room, it would complain about a conflict. Someone has already booked the “new” room even though it should have been held by the initial booking. Alright so how does one re-map this… well took me a while digging through google like this guy, or this guy (seems everyones a blogger these days), but I found an excellent resource blog that covers the problem, and the solution pretty clearly

The Answer

To keep it short for everyone, and as usual to Paraphrase the solution, which so far is not even working for me :@, even after waiting 18 hours. *UPDATE!* Don’t put in X.500 like the stupid UI tells you to… just put in X500 without the ****ing dot… See my Technet post for details!

1)  Open User and Computers (From linked Domain/ Old Domain)
2) Find any User/Resource/Equipment object that were migrated
3) Right Click and select attribute editor tab (requires advanced view)
4) press "L" and lookup LegacyExchangeDN, double click and copy
5) Open Exchange ECP (New Server)
6) Under Recipients double click migrated mailbox, click email address
7) Add new email, Type X500, paste the address you copied in step 4
8) Wait for the OAB to synchronize across the farm and clients

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