Only one of my users are not receiving email notifications only through slack channel.

[Jesus Alfaro]

One of my users are not receiving email notifications since 10/2023. But they do receive notifications through slack that we have integrated. I've checked their email settings and also reviewed our o365 and email protection service and they're not being blocked. Other users are receiving email alerts besides this one user. The email is  jira@mail-us.atlassian.net

[Mohanraj Thangamuthu]

Hello, Good day. Checking from my end noticed the following bounce message for this email. Boune message : relaying denied. Check this mail configuration on mail server as well.