Forum Discussion

Jaycenornin's avatar
Jaycenornin
Copper Contributor
May 20, 2022

New subdomain but e-mail addresses are already in use?

I just created a new subdomain in our M365 for special purpose e-mails & 3rd party mailing support. When I attempt to create a new shared mailbox mailto:address@subdomain.domain.tld I get the error t...
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AndresGorzelany's avatar
AndresGorzelany
MVP
May 20, 2022
Hello,
Is this an Exchange hybrid scenario?
  • Jaycenornin's avatar
    Jaycenornin
    Copper Contributor
    May 20, 2022
    Not hybrid. AAD Connect synced and pw synced (one-way) but not EO hybrid.
    Wouldn't make a difference, tho, since the address@subdomain recipient does not exist anywhere on-prem.
    • Ash_Gardiner's avatar
      Ash_Gardiner
      Iron Contributor
      May 20, 2022
      Hi Jaycenornin,

      What happens if you send an email to this address? Do you get a bounceback notification? If not, can you do a message trace against the test message and see what became of it?
      • Jaycenornin's avatar
        Jaycenornin
        Copper Contributor
        May 27, 2022
        Of course there's an NDR.
        I've already deleted and recreated the DG on-prem in order to free up the address on the subdomain. The work I needed to get done is done.

        The problem is that this is an issue with something in M365 reserving addresses for subdomains. It's not an error or a hidden recipient, it's a thing with how M365 works. I want to know what and why.