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Mail Rejected: SMTP Authentication

AbdulBasith Syed
1 Endorsement
Last Modified: 2017-04-10
I had this question after viewing exchange external email repeatedly blocked/undelivered.

i have a similar issue. my exchange was working good fro past 3 years , but now from past few weeks we are getting rejection messages

Please turn on SMTP Authentication in your mail client. exch2013.kbrokerage.com []:35454 is not permitted to relay through this server without authentication.
A problem occurred while delivering this message to this email address. Try sending this message again. If the problem continues, please contact your helpdesk.

i am unable to find out the reason for this. I tried using a new send connector with smart host and basic authentication. before i was using send connector with MX
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Satish AutiSenior System Administrator

Is your smart host managed by your ISP?
AbdulBasith SyedIT Manager


We have been using the MX record and external DNS. We never used smart host, so basically its not the ISP. i have attached image for the setting we are using  on send connector for the past 3 years
Jude PereraConsultant | Microsoft Cloud Services

Hi AbdulBasith Syed,

Can you try to send the email using OWA? If it gets delivered then it's a client side issue. If the client is using IMAP as connectivity type then ensure that the outgoing server is same as the incoming.

AbdulBasith SyedIT Manager


Hi Jude,
All are exchange clients RPC/HTTP, so there will be no option for outgoing server.  
i dont think IMAP is the issue in my scenario.
its sending through  exch2013.kbrokerage.com, if its IMAP the outgoing server will be imap.kbrokerage.com
Satish AutiSenior System Administrator

Is this problem face by user or have you configure SMTP relay like functional mailbox something like that, for mailing purpose.
Is there any spam filter in you environment?

if possible please share full NDR report.
Satish AutiSenior System Administrator

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AbdulBasith SyedIT Manager


i found the solution.

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