Problem

The notification Report Card and logs indicated 100% successful email delivery, but users didn't receive the email message.

Environment

All versions of xMatters on Demand

Corporate email solutions with security implementations checking for SPAM and malicious messages

Resolution 

xMatters marks an email as delivered when it has been passed to the downstream provider. 

Email domain whitelisting

Corporate e-mail systems often employ DOS sensing due to large volume of incoming messages.  To address this issue, consider whitelisting the xMatters email domains.

xMatters email address domains:
mg.mx.xmatters.com
sg.mx.xmatters.com

IP address whitelisting

xMatters does not recommend whitelisting the IP addresses associated with your xMatters service, for the reasons explained here.

Cause

The corporate email security system is mistakenly sensing valid traffic as a DOS attack due to high volumes of inbound messaging.