If this is an IMAP account, I suggest checking the account online.

I did not help me. Everything about my mails is normal from the 16th May. I can remove a mail. I can delete a mail. But I can't see mails I received before 16th May. Only a very few. I don't know how I made the mails disappea.

Before the mails disappeared I could not remove or delete them. When I opened them they were empty. There was only the headlines.

It sounds like only the index entries remained, giving the impression that the messages were there. If they are not available online, then they are gone.

Any thing I can do to create the missing emails again?

Not to my knowledge.