Your message couldn't be delivered because the recipient's email server (outside Office 365) suspect

Copper Contributor



issue has lasted for months already. First i thought issue was on gmail side (when i tried to reply to emails which were sent from , but now i discovered that i can`t reply to 90% of the emails I have received. Mails are received from different domains and all I try to do is to reply to an email ... What is going on and how to fix this (who can fix this?)!)

Delivery has failed to these recipients or groups:

Your message couldn't be delivered because the recipient's email server (outside Office 365) suspected that your message was spam. 

36 Replies
Hello Raginho

Please confirm if you are experiencing this issue when you send email from OWA ( or outlook desktop client or both.

Also confirm if you have SPF,DKIM and DMARC set up for your domain.

Use the Microsoft header analyzer below to check the message header of the email, to see the spam confidence level (SCL), I suspect that your outbound emails might be leaving through the High risk delivery pool

i am experiencing this issue when replying emails from (through browser) and also via mobile app.

To be precise now, I first noticed this issue when once again was replying to email chain from Cooperative. I had been writing with Cooperative for years and suddenly emails got stuck, so I first thought that issue must be on Gmail side. But now I can`t even reply to travel agent, who has nothing to do with mail address - my mails are blocked.

I have not set up any additional measures for my domain (not even sure what you are talking about :) )

Really need help here .. :(

Thanks for the link!

I checked it and findings were following:

SPF Record Check - no issues reported
DKIM - that i could only check for gmail and not outlook, according to that link...
Only 1 founding: Policy Not Enabled DMARC Quarantine/Reject policy not enabled (mxtoolbox)
but this seems to be okay, as it just shows that there is not additional protections set up..?!


an update reg. the issue.

I now tried to send email to myself (to my gmail account) , just a test email and I can`t even do that. Same error message popping up once again.

What on earth is going on? Anybody??

Dear Raginho

Is it possible if you could provide a screenshot of the error message?

so this discussion just suggested to check blocked and safe senders list.

This really can`t be the right solution. How come i can`t reply to travel agent who email me first time? (in addition to other examples i had.. ).


Unfortunately, if you have been added to the spam list by other users, all Office 365 users will reject your mail automatically.

Fix email sync issues (


care to reword this explanation as I am not quite following!?
Which other users might have added me to spam list? You mean user who I am trying to email?


Yes, if you send messages to many users and they mark them as spam, then you are automatically included in the list of senders with a bad reputation.

Right, i totally understand.

And this really can`t be the case here.
I have been having the exact same issue since about last week and there is no-way I have been added to any spam list as I rarely ever send emails, this started when I tried to reply to an agency who is helping me move house, it wouldnt le me email him and now i realized i can barely email anyone, not even my dad. My email address has become useless now
I wonder who can help me and @Davidmc1984 here.. or what is really the explanation here.

I almost feel that someone is trying to hijack my mail address (so that I would abandon it ..)


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Only Microsoft technical support is appropriate, the MTC public forum is not Microsoft technical support.

Hi @Davidmc1984 

Please refer to this article, check if your messages are sent as plain text or HTML. - this can also be the cause of problems.

Sender Support in (

How should I contact MS tech support? Through which channels?



Please you can fill out the form, it will definitely be a step that will clarify whether you are on the list of blocked senders, but you will not receive a response immediately it may take a while.

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