Unannounced Changes - EXO PER-MAILBOX Recipient Limit (Maximum Recipients)

Frequent Contributor

I'm just wondering if any other customers noticed that this setting was suddenly enabled for customer control.  Anyone?  We actually started using it and added the step of setting this to 0 as part of our steps for dealing with a compromised email account.


All of a sudden this morning, the setting is greyed out in the GUI, box check, setting at 500.  In PowerShell the parameter is gone from the Set-Mailbox cmdlet.


There's a User Voice for this and it says "Working on it" since July 2019.  Well, that translates to "we're making changes without doing notifications".  I could supply my admin audit logs to Microsoft to prove this.  In fact, I'll generalize the log entries and share them shortly.

4 Replies
best response confirmed by Jeremy Bradshaw (Frequent Contributor)

It appeared on the Roadmap few days back, still marked as In development and targeted for next year.

Ahh, I see that, here's the roadmap item for anyone wondering:

Tenant Customizable Recipient Limits

In Exchange Online a mailbox user is allowed to send to a maximum of 500 recipients per message. This default value currently can’t be changed by the tenant admin. Yet, many admins would like to raise this limit on at least a few mailboxes (for monthly newsletters for example). Others want to significantly lower it (to, say, 50 or some such) for most or all mailboxes in their organization, as part of a perceived defense-in-depth strategy to reduce the potential impact should a hacker compromise a user account and start blasting out spam, or a disgruntled employee tries to air their grievances company-wide. With the upcoming customizable recipient limits, you’ll now be able to customize this setting between 1 and 1000, for a single mailbox, multiple mailboxes, and for the default setting for new mailboxes that you create in the future. Single and bulk edit will be available in the Exchange Admin Center UI, while customizing the default setting for new mailboxes can be done via Remote PowerShell.

Featured ID: 55025
Added to Roadmap: 9/6/2019
Last Modified: 9/6/2019
Tags: All environments, Exchange, General Availability
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Must be getting developed in production...


Just adding in my gripe that the planned allowed values of 1 through 1000 - seems off the wall to me.  Why not allow 0, especially when you're allowing twice the current maximum for the upper limit?  It's just inconsistent and I hope that you will allow 0 in the end.  0 works fine when it's allowed.


Well it went live, and still I am confused on the reasoning for the minimum setting of 1 instead of 0.  It feels like a tease, having this feature finally enabled, only to just miss my personal reason for its need in the first place.  :facepalm: