Exchange Pop3 LIST not showing all mails

Hello community,

anybody got an idea for following problem:

We have a exchange 2016 CU23, pop3 is enabled. 

When I try pop3 over telnet and issue a list command, no mails are displays. When I enter the same mailbox via owa, i can see multiple mails.

Any idea? I cant fetch those mails via pop3. 

The strange thing: This only happens to ~2 out of 50 Mails, which a correctly fetched. I can't find any difference in those mails. When i save the mail as .eml and import it in the mailbox back, I can fetch it via pop3.

br

Chris