Technically explain why some emails don't arrive destination

[Sattar]

Hi.

Sometimes, some emails don't arrive to destination (Sometimes email forwarders don't work correctly)

Technically, what is the reason? Is it a server crash? or spam filtering or what?

How to fix it and find out the exact reason for each email? It's very important to figure out whether some specific emails are arrived or not.

Thanks.

 

[Infopro]

These posts should be of some use to you:

Why didn't my email get delivered? or where did my email go?
Reading and Understanding the exim main_log