Exchange Online to introduce External Recipient Rate Limit

Hi chrismilton, the linked page you gave mentions:

We approve higher limits for customers based on use case requirements, domain reputation, traffic patterns, and failure rates. To request higher limits, follow the instructions at Quota increase for email domains. Higher quotas are only available for verified custom domains, not Azure-managed domains.

I have never gone through that process yet as we are just preparing internally to use this service, hopefully at a scale way way way beyond 100/hour or 30/minute.  Would be nice to hear from a live human that they succeeded at getting their quota raised way up and it wasn't a hassle nor a repeating requirement.

The way ACS has been designed, particularly with where you grant an Entra ID app/SPN access (on the ACS resource, which has "connected" domains that live within ECS resources, and which have specified sender addresses within them) is, to me, an even bigger joy-destroyer.  If you have a certain custom domain that you want multiple teams to use for their sender domain, but you want them to each use their own specific sender addresses, you have to add that domain to as many different ACS+ECS resources as there are separate teams, and then add just the approved sender addresses into the corresponding teams' ECS resource, then connect that domain to their ACS resource.  For each ECS you have to add domain verification TXT records to add.  Also if you have an SPF that the ACS SPF checker doesn't like, you won't be able to use that domain until you modify the SPF.  Up until just recently, you couldn't connect more than one domain at a time to any single ACS.

So ACS is clearly very limited by design, I think as a security-based attempt to discourage bad actors from using the service for illegitimate purposes.  As long as increasing the quota is a smooth and easy process for legitimate customers, and wishfully hoping they redesign how the permissions are granted, it should hopefully still be adequate to avoid having to use something 3rd party like SendGrid.

In case anyone is listening, it would have been nice if ACS email's design was so that sender addresses were the things that are 'connected' to ACS resources, allowing us to add domains 1 time only, and then permit different teams (their Entra ID app(s)) access to a custom list of sender addresses.  In a big org, with the current design, we'll be creating temporary TXT domain ownership verification records for the same domains, 100's of times, 1000's of times over a couple of years, for the same domains, over and over....