New Shared Mailbox - getting error when sending emails

Question

Hi all,&nbsp;wondering whether you may help me to understand the behavior that I experience recently with new shared mailbox in O365 created recently...&nbsp;I have never had problem to create shared mailbox in Exchange Online before... However, recently I had to create a new shared mailbox and assign full access &amp; send as permission for few users. Strangely, when those users tried to send email from that mailbox, they received the error - picture attached&nbsp;The mailbox is set up the same way as all my shared mailboxes in the past... It looks like any that I create recently (last two weeks) it is behaving the same. Also, I can see that Outlook is trying to send the emails like "sent on behalf" which is strange as "sent on behalf" is not set for the users.&nbsp;PS: I created a shared mailbox 2 weeks ago and ended up to make it standard user mailbox and adding it manually to outlook for required users... I thought there was just something "strange" going on with that mailbox.... but today I had to create another one and it is the same.&nbsp;PS2: all shared mailboxes that were created in the past do not have any issue and work fine...&nbsp;

vasilmichev · Answer

Are you trying to send to external users? Which server is generating the NDR, Exchange Online or the recipient's? It doesn't look like it's Exchange Online, and the code itself suggests a mail flow issue, not something specific to the shared mailbox or permissions on it.
What does a message trace show?

misum83 · Answer

Hi Vasil,I will create a testing shared mailbox to play with it... Email is sent to external recipient, yes. I do not believe it is mail flow or similar as that would affect all maliboxes.... however... as I mentioned... all mailboxes (even shared ones) are working fine... Except the shared ones that were creating recetly.I've found a topic a guy described the same situation ... and looks like with MS tech support they got it fixed by removing permissions / re-adding permission / disabling automap (all these via PowerShell) and manually adding shared mailbox in Outlook....So I will try that as well... However, still wondering why this is happening 😕

misum83 · Answer

Just to let you know..Eventually, I've found out that the user who was testing shared mailbox made a small "typo" in the shared mailbox email address which causes this issue for him.... 😕So all seems to be fine....

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New Shared Mailbox - getting error when sending emails