Mailgun emails are rejected by Zoho

Mailgun emails are rejected by Zoho

It used to work in the past, but only now I found out that emails are not coming through any more.

According to the logs from Mailgun, the messages are rejected by mx.zoho.com with error code 541 and message "5.4.1 Mail rejected by destination domain".

I have checked my Zoho spam settings and even tried white listing the sender domain without success.

Please help!