Issue with receiving emails

We are having issue receiving emails.

One in particular is our domain registrar, they are unable to send email to our account & are saying the mails are unresolved.

The have sent on the following from a mail they sent which we did not receive.

ping mail.rathgarconsultancy.com
PING business.zoho.com (8.39.54.59) 56(84) bytes of data.
^C
--- business.zoho.com ping statistics ---
16 packets transmitted, 0 received, 100% packet loss, time 15337ms

Can you please let us know what needs to be done to resolve this issue.

Kind Regards