Update 6/11/2025: We updated the timeline of this deprecation mentioned in this post.
Exchange Online will permanently remove support for Basic authentication with Client Submission (SMTP AUTH) gra...
Updated Jun 12, 2025
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Manish-StrategicPM
Microsoft
MicrosoftNumerous customers have approached the ACS email team with requests for shorter usernames for SMTP authentication. Currently, the format for SMTP usernames is: ""<Azure Communication Services Resource name>|<Entra Application Id>|<Entra Application Tenant Id>". However, there are legacy applications interfacing with ACS over SMTP that are constrained by a 40-character limit for usernames, which makes the lengthy ACS email username format a significant barrier to adopting our service.
To address this issue, our team is committed to developing a solution for shorter usernames for SMTP authentication. By January 2025, we expect to launch a private preview that will allow select customers to utilize shortened usernames for establishing connections to ACS, on the condition that their ACS and email service configurations are complete and operational. This feature will allow applications to define their usernames with less characters and even use email-id as usernames.
Once we launch the feature in public preview, I will post the details in this forum.
Manish-StrategicPMany update you can share on the private preview?
If you can use HVE use it, it wasn’t too terrible to setup. The hardest part was figuring out which settings were needed on the device and what went where since each device is different.
HVE has a limit of 2,000 messages, which works as expected for some scenarios. However, HVE is in Preview and not available with endpoints in Europe (AFAIK), making it unsuitable for many other scenarios.
