Update 7/14/2025: Updated the FAQ.
As with all cloud services, Exchange Online imposes service limits to prevent misuse of Exchange Online resources and ensure availability for all users. For examp...
Updated Jul 14, 2025
Version 18.0
Blog Post
The short window for this is really un-acceptable. This blog post was made on 2/24, and I just got the admin notice from O365 today on 3/4, leaving us approx. three weeks to take care of clients, some who will be directly impacted by this and have legitimate business needs to send large volumes of e-mail. We had the MERRL on our radar:
Exchange Online to introduce External Recipient Rate Limit | Microsoft Community Hub
But thought we had time to deal with it (Oct of 2025). Now we have three weeks? Did anyone at Microsoft consider that a lot of systems / software send e-mail through SMTP, while Azure Communications uses a REST API, which the sending system/software may not support (I did not see where one could define a SMTP connecter in Azure Communications)?
A three week timeframe for people to adjust in many cases will simply be un-workable.
Really getting to dislike Microsoft services more and more, especially when things like this keep popping up.
KevinShaughnessy
Microsoft
MicrosoftJames Dettman ACS does support SMTP. I asked Copilot about SMTP support in ACS email and it gave me these links, confirmed with the ACS team these are good references for how it works.
How to use SMTP to send an email with Azure Communication Services. - An Azure Communication Services quick start guide. | Microsoft Learn
Weird that I didn't come across this earlier in checking.
Thanks for that. Takes some of the worry out of this.
Jim.