We are facing below mentioned issue post recent build 9336 - Changed: A setting to perform SMTP AUTH MATCH checks against message headers in addition to MAIL FROM.

Irrespective of selecting domain or email in Require Auth Match, there is increasing logging and blocks in smtp logs with error as below

[2025.08.07] 15:15:28.253 [xx.xx.xx.xx][47207335] cmd: MAIL FROM: <>

[2025.08.07] 15:15:28.254 [xx.xx.xx.xx][47207335] senderEmail(1): 

07] 15:15:28.256 [xx.xx.xx.xx][47207335] rsp: 550 From domain must match authenticated domain | Info: domain [abc.com] (1), authenticated username: xyz@abc.com, MAIL FROM: [2025.08.
[2025.08.07] 15:15:28.256 [xx.xx.xx.xx][47207335] disconnected at 8/7/2025 3:15:28 PM

When we check user outlook - then all fields including FROM is properly filled with Name or email id, to confirm, sending email id is the same as smtp authenticated user id.

Then from where MAIL FROM <> blank is pickin up in the log which further creates the issue if IP getting blocked, as if now we have tweaked the rules which prevents the IP blocking.

If any one can refer their smtp logs and facing such issue and is this SM related bug or Outlook related bug, what we have seen is above with users using O365, Outlook 2019, Outlook 2016

Thank You

HBS