Level 1: Cadet

Bounce backs (Office 365)



We have a client who is using email services with Office 365, when ever the client emails email addressess a bounce back is received. We have been unable to resolve this with support from Microsoft, any ideas why this would be occuring? 


Bounce back is below:


More Info for Email Admins      

Status code: 550 5.7.350

When Office 365 tried to send the message to the recipient (outside Office 365), the recipient's email server (or email filtering service) suspected the sender's message is spam.

If the sender can't fix the problem by modifying their message, contact the recipient's email admin and ask them to add your domain name, or the sender's email address, to their list of allowed senders.

Although the sender may be able to alter the message contents to fix this issue, it's likely that only the recipient's email admin can fix this problem. Unfortunately, Office 365 Support is unlikely to be able to help fix these kinds of externally reported errors.

Error Details   

Reported error:  550 5.7.350 Remote server returned message detected as spam -> 550 <******> recipient rejected. IB603a  

DSN generated by:       

Remote server:     


Message Hops    

HOP      TIME (UTC)       FROM     TO       WITH     RELAY TIME      

1        6/14/2017
11:35:36 PM        mapi     *       

2        6/14/2017
11:35:37 PM        Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256)        1 sec   



Any assistance would be appreciated.




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Level 13: Super Sleuth

Re: Bounce backs (Office 365)

My office is using Office365 email hosting with Exchange Online and I've just emailed my personal Bigpond account without any issue.
What is the subject and content of the messages like that are being sent?  Is there any chance that they could be suspected of spammy content?

You should also check the domain to make sure it's not on any real-time black lists (
While you're at it, you ask them to BCC you in on one of the problem email sends so you can analyse the message headers.  It could be that their SPF record, DKIM or DMARC is causing Bigpond's stupidly sensitive email platform to reject the messages.

I need IDDQD and IDKFA in real life.
Level 1: Cadet

Re: Bounce backs (Office 365)

I have 2 customer that have experience the same issue, but only on a single Bigpond address. I suspect that Bigpond customer (receiver) had the Telstra Protection subscription. 


My first Customer is a business on Office 365, fully setup with SPF and DKIM activated and validated. 


The other one is on Hotmail.


Both situation, only 1 of their contact on Bigpond is rejecting their messages, not their other contacts on Bigpond. 


Very curious.

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