Lost email messages

[Kevy]

I am getting emails from one place and the email has "Unknown sender" in the
"FROM " field, shows the subject ok, then says."The message could not be
found" My ISP says it is the senders problem, the sender says all is fine at
their end.Can anyone help please?

 

[Gary VanderMolen]

If you only have this problem with one sender, then most likely the problem
is at that sender's end.