Exchange Online Not Receiving from Only One Domain

[zwethuko]

Dear, 

We have migrated one service provider mail eg (online.com) to M365. 

Exchange Online can be received from other external domains but can't receive from only that one service provider mail (online.com).

I traced mail flow from exchange > not received from (online.com) but outgoing is ok.

Is there any way to track mail flow to prove Exchange Online is not received from that mail service provider (online.com).

M365 to Online.com is ok.

Online to M365 is not ok.

Thanks

[#2 · Accepted solution]

You probably have some traces left of your domain/recipients with the previous provider, check things on their end or open a case with their support.

[#3]

Yes, bro, I'll check with their mail host provider.