The Email delivery logs say "retry timeout exceeded".
When the delivery log lists "retry timeout exceeded", that message was not delivered.
We try to deliver again in 20 minutes, 40 minutes, 60 minutes, etc.
However, the temporary error happened each time we tried.
After 3 days of continuous delivery attempts, we stop trying to deliver. That’s when the delivery logs will indicate the retry timeout exceeded error.
Copy/paste the delivery logs and send to your Subscriber. Ask them to work with their ISP to correct the problem.
We find the best solution is for the ISP to whitelist our email servers. This normally prevents future delivery problems.
Our IP addresses are listed on our website. Instructions are included for how to whitelist our servers.