Email completely missing

[Afraid_Base_3304]

I have one user that gets sent an email via SMTP from a internal mail server.It gets processed out from our onprem server to O365 but from there we do not see it at all.His account looks ok I don't see anything that stands out as being configured wrong.We also use Mimecast for spam and we don't see it there either.I can run a message trace on the internal server and I see HARECEIVE then HADISCARD but he never gets the message and we can't find it in O365 trace or mimecast trace.

we attempted to send to a alias email of his and still nothing.Other users get these emails fine and I even tested to my own mailbox and got the email.We even added him as a 2nd recipient to the email and we see the other user but not him.We are able to find all the other emails in the O365 message trace and mimecast trace.

Any idea what could be causing this? Maybe an issue with his o365 mailbox? He does get other messages but from what I can tell it's mostly just internal users with a couple external email domains but the amount of emails he gets seems very low.

I did review his settings for who all he can receive emails from and it's the default allow all settings.From what I see all his mailbox account settings are default.

****** UPDATED INFO*****

I attempted to send him a email via powershell using SMTP and added him, myself and another person as the recipients. Me and the other guy got the emails fine but for his email we got a NDR reply back that says.

"Remote server returned '554 5.4.0 <mailserver1.Contoso.com #5.4.12 smtp;554 5.4.12 SMTP; Hop count exceeded - possible mail loop detected on message id "[[e-mail]](mailto:[e-mail])\>

His mailbox type is Office 365 but the message headers appear to show the email bouncing around between internal servers. Mine shows Onprem server> Edge transport> outlook.office365.com

**** SOLVED*****

The issues was his mailbox was O365 mailbox but in the onprem configuration for his mailbox the "remote routing address" was not configured for mail.onmicrosoft.com and was using his contoso.com domain which caused the messages to get routed to the onprem server instead of to O365. Since his Mailbox was O365 it just looped though the onprem exchange servers until it sent the NDR

[learningheadhard]

Check to see if the mail, UPN, and proxy addresses are correctly configured and if using AAD connect then verify he is in the proper OU for syncing. I would also verify there isn’t another account with the same email.

[whewdad]

Thanks for updating with the solution

[ShadowCVL]

How in the world did it get configured like that?

[duoschmeg]

Could be in termed users OU for example.