Exchange distribution group migration… remember the Outlook cache
Outlook caches the X500 address (aka LegacyExchangeDN attribute) of a Distribution Group object.
So, when you migrate a distribution group, remember to not only bind the SMTP address to the destination Distribution Group, but also the X500 address (available as the LegacyExchangeDN attribute value) of the old distribution group, as an additional Email address for the destination distribution group.
Forgot to grab that LegacyExchangeDN attribute value before removing the old distribution group? Don’t worry. Have someone with the cached entry in their Outlook send an email to the old distribution group, and they will get an NDR.
This NDR will contain something similar to the following:
IMCEAEX-_O=FIRST+20ORGANIZATION_OU=First+20Administrative+20Group_cn=Recipients_cnfirstname.lastname@example.org #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
You can create an X500 Email address from this information and add it as an Email address on the destination/new distribution group.
As described in KB2807779, simply take that string and perform the following:
- Replace any underscore character (_) with a slash character (/).
- Replace “+20” with a blank space.
- Replace “+28” with an opening parenthesis character.
- Replace “+29” with a closing parenthesis character.
- Delete the “IMCEAEX-” string.
- Delete the “@contoso.corp” string.
Note that any character is just ASCII encoded, so an underscore is +5F, etc.
In the above example’s X500 address would be:
/O=FIRST ORGANIZATION/OU=First Administrative Group/cn=Recipients/cn=olddistrogroup
You can assign this additional Email address (aka alias) to the distribution group through the distribution group properties Email Address tab in the Exchange Management Console (use Email type: “x500”, and the Email address as above), or via the `set-distributiongroup newdistrubiongroup -emailaddresses [list of email addresses]` powershell command. Note that you should use `get-distribitiongroup newdistributiongroup | select emailaddresses` to see the existing entries, then set-distributiongroup…` with the input including the existing entries.
Once the X500 address is bound to the new distribution group, re-test with the cached address and you should be good.