See article about incoming email filtering: https://wiki.cerge-ei.cz/doku.php?id=public:emai:spam_chain|
It is important that the individual reports the problem or situation in a descriptive way, gives useful details, mentions the observed circumstances and invests at least some effort to the basic troubleshooting.
Well reported and documented issue may greatly shorten the overal time of the processing.
Please try to find and report as many details as possible by the following hints:
Specifically for the lost messages or undeliveries, collect at least these facts:
Copy-paste the header part as a plain text to the email sent to helpdesk