'send as' from an SMTP alias on a shared subdomain mailbox

Question

Consider a shared mailbox that exists in a company primary domain

testing@contoso.com

Now add a subdomain to your tenancy:

developers.contoso.com

Set the subdomain as InternalRelay rather than Authoritative

Now add a catch all mail flow rule:

All mail to @developers.contoso.com forwards to 'testing@contoso.com'

Now delegate the test@contoso.com mailbox to those who need it.

Test the system and it all works exactly as designed.

And here's the kicker, the developers want an option to be able to 'Send As' name@developers.contoso.com

So I think fine, add that as an SMTP alias to the mailbox, check that the developers have both delegation options (send as/full access)

But yet trying to send as that address results in an error response with "You do not have permission to send the message on behalf of the specified user."

Initial thought was to leave it alone for an hour, let Exchange sort itself out. Still no joy.

I'm missing something, but I can't think what. Any suggestions?

Answer 1

Hi @Rob Brown ,

Just want to confirm that you want to send as name@developers.contoso.com from a user mailbox instead of a shared mailbox.

If in this case, Did you manually enter the email address directly in the FROM box?

It is recommended that you try the following steps to send a test message to see if that works:

1.       Open a new message.

2.       Click on the "From" option to open GAL.

3.       Select the desired email address from the GAL.

4.       Send the test email.

Hope the above method helps you.If there's anything else we can help, feel free to let us know.

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Answer 2

Addendum:

It fails to send from both Outlook and OWA when trying to use the specific address.

It's now over 24 hours since the last set of changes and the address in question is visible in the GAL.

Still not sure why it's blocking.