I have an Exchange Server 2019 on premises working as our mail company server. Some users can't (others can) send mails via SMPT port 25. Is not an Open relay, the problem was sending internal an external destinations.
This is the result from smtp test at https://www.gmass.co/smtp-test
220 mail.mydomain.com Microsoft ESMTP MAIL Service ready at Tue, 13 Sep 2022 21:09:25 ?
EHLO [172.31.1.116]
250-mail.mydomain.com Hello [xxx.xxx.xxx.xxx]
250-SIZE 37748736
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-AUTH LOGIN
250-8BITMIME
250-BINARYMIME
250-CHUNKING
250 SMTPUTF8
AUTH LOGIN
334 [xxx]
[xxx]
334 [xxx]
[xxx]
235 2.7.0 Authentication successful
MAIL FROM:<myuser@mydomain.com> SIZE=554
RCPT TO:<anotheruser@mydomain.com>
250 2.1.0 Sender OK
250 2.1.5 Recipient OK
DATA
354 Start mail input; end with <CRLF>.<CRLF>
From: myuser@mydomain.com
Date: Tue, 13 Sep 2022 19:09:19 ?
Subject: SMTP test from mail.mydomain.com
Message-Id: <507S7CPHVHU4.D86IGJWU6VG32@WIN-AUIR3RRGP88>
To: anotheruser@mydomain.com
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="=-It6fjVK5MLh5hmyoGNPCPg=="
--=-It6fjVK5MLh5hmyoGNPCPg==
Content-Type: text/plain; charset=utf-8
Test message
--=-It6fjVK5MLh5hmyoGNPCPg==
Content-Type: text/html; charset=utf-8
Content-Id: <507S7CPHVHU4.5IUQIQGPZEUA2@WIN-AUIR3RRGP88>
<b>Test message</b>
--=-It6fjVK5MLh5hmyoGNPCPg==--
.
**550 5.7.60 SMTP; Client does not have permissions to send as this sender**
RSET
250 2.0.0 Resetting
But with other users the result is:
250 2.6.0 <WB6MM4SHVHU4.ZVXOEXV0CG8U@WIN-AUIR3RRGP88> [InternalId=62423054680070, Hostname=myhostname] 1618 bytes in 0.332, 4,754 KB/sec Queued mail for delivery
I have tried deleting the user, recreating it and reassigning the mailbox, but it doesn't work.
Any idea? Thanks for your time!