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We are using the email portion of Azure Communication Services to send email from an application. It is working to send from our own domain to everyone at a customer domain except for 1 user. It looks like we emailed the user before the account setup was complete so it bounced with a 5.1.1 error (no such mailbox). I'd expect that first error. However, now that the account is working properly (we can email them from other external domains), it continues to return a 5.1.1 error. It's as if the ACS has remembered the error and cached it - so it's no longer retrying.
Has anyone experienced anything like this before?
@Dean Landry when did you start noticing this behavior? is their domain different from the other customers?
The issue you're facing is likely due to the way Azure Communication Services (ACS) handles email delivery and bounces. When an email is sent to an invalid or non-existent recipient, ACS marks that recipient as a hard bounce, which means that subsequent attempts to send emails to that recipient will be automatically rejected without retrying.
This behavior is designed to prevent spam and reduce the load on the email servers, but it can cause problems in situations like the one you're experiencing, where the recipient's mailbox becomes valid after the initial bounce.
We have lots of other emails going to that customer's domain (and many other domains) without issues. I've discovered that we sent the user an email the day their email account was created, so I'm thinking we likely emailed before mailbox setup was complete -- they use GoDaddy Office 365 and I've seen delays with account creation on their service before. So now they're likely in the Managed Suppression List for 14 days.
I'm guessing the only solution is to wait 14 days to email them or to have them use an alias for this user with out product.
yes, that is correct. but it might be faster for them to create an alias for the user instead of waiting for 14 days but if the issue persists after 14 days please do let us know