DB mail was working fine using SQL Server 2014; however since we moved our email to Office365 online Exchange, we are having issue. Whenever there are rapidly generated emails by our application; then sending emails is stopped with following message:
The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 3 (2018-04-08T08:25:06).
Exception Message: Cannot send mails to mail server. (Failure sending mail.)
Service again starts sending emails automatically after a lag of few hours.
I have already checked email account separately and it is working fine.
This is a limit set by Office 365
. Check this image captured from microsoft technet post
Based on your subscription, limits are there for sending total emails per day as well as bulk email at a time. Same has been confirmed in this Microsoft blog question
That's why your task stops sending email for sometime to reset its Recipient limit.