Email Communication issue with specific (domain) after migration to AWS

We've recently moved our operations to AWS, but we're encountering a problem with receiving emails from one particular client domain (www.systeral.com). While they can receive emails from us, we're not receiving their replies. Interestingly, all other clients are able to send us replies without any issues.

*So far we have tried filtering the Ip address of this domain in SES filters and allowed the IP. *we have also tried disabling the TLS incase the the domain was not using authenticated channel but unfortunately nothing has helped. *we have kept an eye on junk/spam folders but theres nothing. *we also activated the event logging but we dont see email communication from this specific domain has someone faced the similar situation before ?