Office 365 calendar invites not going through to recipient

I have an office 365 user where their calendar invites are not going through to the recipients.  I can send emails from the account, but calendar invites do not make it through.  The calendar invite is in the Sent folder, but never makes it to the recipient.
Jeff McNallyAsked:
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timgreen7077Exchange EngineerCommented:
does this happen with any recipient or only certain ones.
Saif ShaikhServer engineer Commented:
Kindly try in OWA and see whether the calendar invite gets delivered to other recipient.

Log in into the O365 admin portal using global admin credentials and check the service health for any advisories on exchange or calendar issues.
Jeff McNallyAuthor Commented:
timgreen7077 - I'm aware of it only happening to this one user.  In fact, they actually have a 2nd O365 account, and that has no issues.
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Jeff McNallyAuthor Commented:
Saif Shaikh - I tested the email from his account sending invites to my own, both from the Outlook application and OWA.

Also - I'm seeing no issues within the service health from the O365 admin.
timgreen7077Exchange EngineerCommented:
If this is only happening to a single recipient, verify that the recipient doesn't have any rules for this sender. Also does the sender get any errors when attempting to send?
Saif ShaikhServer engineer Commented:
Can you please provide us screenshot of the errors in service health from the O365 admin. Also is this happening for a single user or mutiple as Tim said.
Jeff McNallyAuthor Commented:
The recipient, in this case, me, does not have any rules for this sender.

The sender gets no error messages, to them it looks like it went through. It's in the Sent folder.

I'm baffled.
timgreen7077Exchange EngineerCommented:
are you both in o365?
Jeff McNallyAuthor Commented:
Yes we are both O365 users in the same tenant.  Although, his account is a different domain
timgreen7077Exchange EngineerCommented:
can you run a message trace in o365 to see if it shows that it was delivered or not
Jeff McNallyAuthor Commented:
I found this error - this was from the Meeting request to me.

Looking for the NDR that was sent to his email.  Haven't found it yet.
Jeff McNallyAuthor Commented:
I found the NDR email.  He has some online Outlook rules that were moving all emails addressed to him in to an RSS folder.  I've deleted those rules.  Here's what his email said:

Delivery has failed to these recipients or groups:
Your message couldn't be delivered because you weren't recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it's no longer allowed to send messages outside of your organization. Contact your email admin for assistance.
Saif ShaikhServer engineer Commented:
Try whistling the email domain in Outlook so that it does not mark it as spam and gets delivered to user inbox.

Select the “Home” menu, then select “Junk” > “Junk E-mail Options“.
Select the “Blocked Senders” tab.
Choose “Add…“.
In the “Enter an e-mail address or Internet domain name to be added to the list” box, enter the name or address that you want to add. ...
Select “OK” when you are done.
timgreen7077Exchange EngineerCommented:
Ok, since you removed the RSS rules does that resolve the issue?
Jeff McNallyAuthor Commented:
timgreen7077 - no it did not.  

From what I understood from that error message, it looks like Microsoft has tagged him as a spammer and blocked his outgoing emails. I'm not sure how to resolve that. He has been the 'victim' of a number of phishing attacks.  He's not very good at recognizing them.

In the meantime, I created a new account for him and will be shutting down the old one soon.
timgreen7077Exchange EngineerCommented:

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Jeff McNallyAuthor Commented:
Thank you for your help on this.  The message trace was new to me and very helpful.  It wasn't until then that I was able to really trace what was happening.

Thank you.
timgreen7077Exchange EngineerCommented:
Glad it helped.
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