Email Sending issue!

Email Sending issue!

One our our email account (acc*****@s3india.com) is facing following issues from today itself while sending mails.
1. Hourly Ratelimited. Notification mail sent
2. rejected due to usertype=REPUTATION_HIGH_USER rlResult=PERMFAIL
3. 5.3.4 message size limit exceeded (message side is with 15MB)

Kindly resolve this on an highly  urgent basis.