not receiving emails from a particular sender

[AVG51]

In the past week I haven't been receiving emails from a particular sender. Messages from them have not been going into my inbox, or trash or spam folders. The sender has been able to receive messages from me, but their replies have not been getting to me.

Is there some way to check whether the messages are being blocked somewhere before they reach me? Can something be done about it?

[Ady-TalkTalk]

Hi AVG51, I've run a 7 day scan using the email address you registered with, but it shows nothing. Please send me a personal message with the full sender email address so that I run a check on it. 

Ady

[Gondola]

What's the sending domain? That's just the part of their email address after the @ symbol that I'd need to check for you.