Missing mail Trash

Log into the web Interface of the mail server with the Browser of choice.

If the Mail Trash folders on the Mail Server there ?

Is the mail server using IMAP Protocol or POP Protocol ?

If IMAP protocol is used, whatever is showing on the Mail Severs will be reflected in Mail (Mail Client )

Sometimes a " Rebuild " from within the Apple Mail Application may work.

Depending on how may e-mail are involved, this could take some time so be patient

refer to image below