Username length issue with SMTP in Azure Communication Services

Question

Hi,

I'm testing "Email SMTP as a Service" that is in preview within "Azure Communication Services". I was so excited to hear about it because we've just done an Exchange migration to O365, and this feature will help mop up the remaining SMTP client apps without having to deploy any SMTP relay infrastructure.
It was very easy to set up and get working for 2 test domains.... BUT...

The instructions state that a Service Principal must be used as the user. And with this, the username must be in the following format:
<Azure Communication Services Resource name>|<Entra Application ID>|<Entra Tenant ID>

This makes for a super long username. Mine was 94 characters! It worked in one SMTP client software but others I've tested have character length limits such as 60 characters.

The 2 pipes (or dots), App ID and Tenant ID guids mean that the username has 74 characters before the ACS resource name prefix is added!

I thought it might work with a UPN as username, so I added a user to the IAM Role Assignment, but that didn't work, returning error code "535 5.7.3 Authentication unsuccessful".

Is there a workaround? Because without one, the use of this SMTP feature will be severely limited.

Thanks,

Jonny S

Answer 1

@Jonny Sharp Good news! The product group wants me to gather some information from you so they can look into whether or not it would be possible to address this limitation.

Can you please send me an email to azcommunity@microsoft.com with the subject as ATTN: Bryan. I will then reply with the information we need for the product group to begin their consideration.

Answer 2

I'm facing a Kyocera vendor SMTP 64 character limit for username as well. :( All the effort to get the things working, to find this the blocker.

Answer 3

I have exactly the same issue in UniFlow, Canon printers and in Navision(basically all my SMTP use cases).

I would assume that the length of the username AND password is going to be a major issue pretty much in majority of the applications where this could be used.

Answer 4

@brtrach-MSFT , any news regarding the character length issue for the username? We have some large enterprise customers willing to test the Azure Communication services relay functionality but this is a blocker for them. Especially printers have a character length limit of 64 characters for username field but as others already mentioned other applications have similar restrictions. This needs to be addressed to make this product usable.

Answer 5

I have similar needs looking to use ACS as a SMTP solution for devices that don't support modern authentication. An example is a Dell iDRAC which appears to have a 50 character username limit.

If I only include the <Entra Application ID>|<Entra Tenant ID> component of the ACS username I am seeing 75 characters which makes it useless for this purpose. As I created a descriptive <Azure Communication Services Resource name> the combined total of my username came to 111 humorous characters.