Your message wasn’t delivered to anyone because there are too many recipients.

Scenario: A user with a Exchange Online receives the following error: “Your message wasn’t delivered to anyone because there are too many recipients. The limit is 0. Your message has 1 recipients.“

Investigation:

In Exchange Online, check the RecipientLimits on the mailbox: get-mailbox steveman | Select RecipientLimits

Fix: If not set correctly, run the following: set-mailbox -recipientlimits 500

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If Hybrid, also check the remote mailbox in Exchange On-Premises: get-remotemailbox steveman | Select RecipientLimits

Fix: If not set correctly, run the following (AD PowerShell):
Set-ADUser steveman -Replace @{msexchRecipLimit=”500″}

Note: There is no set-remotemailbox -recipientlimits, this is why you need to perform this using AD PowerShell