Out of curiosity i did one testing that if an external sender sends an emails to a distribution group or dynamic distribution group which is only accepting emails from subset of users allowed, then whether that works based on mail-from or header from field.

In rest of the article, I will explain about the test performed and it helped to find me an answer :

Scenario :

  •  Distribution Group Name – testdl@learn4coming.xyz
  • Allowed Sender – powerusr@learn4coming.xyz

Let’s look into header of two emails, Based on the testing exchange online accepts email from ‘From’ header, hence an email which has matching mail-from but from is different that get undelivered.

  • This email won’t get delivered because from field isn’t matching allowed user powerusr@learn4coming.xyz.

telnet smtpserver.fqdn.com 25
ehlo sj
mail from:powerusr@learn4coming.xyz
250 2.1.0 Sender ok
rcpt to:testdl@learn4coming.xyz
250 2.1.5 Recipient ok
data
354 Enter mail, end with “.” on a line by itself
From: Admin <admin@learn4coming.xyz>
To:testdl@learn4coming.xyz
Subject: from is admin

data

  • This email will get delivered because from field IS matching allowed user powerusr@learn4coming.xyz.

telnet smtpserver.fqdn.com 25
ehlo sj
mail from:admin@learn4coming.xyz
250 2.1.0 Sender ok
rcpt to:testdl@learn4coming.xyz
250 2.1.5 Recipient ok
data
354 Enter mail, end with “.” on a line by itself
From: Sourabh <powerusr@learn4coming.xyz>
To:testdl@learn4coming.xyz
Subject: from is powerusr

data

  • With this, we have confirmed that From Field is important if you are sending email to a restricted distribution group, which is controlling email sending rights based on allowed senders.

Thanks you reading !

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