yes, I knowHello,
The "internal" data was a message used by wu-imapd to store inbox information. It wasn't even really important for wu-imapd.
It has zero relevance for dovecot.
It's completely safe to delete, especially if you're running dovecot.
but I some of my customers check mails everyday using imap and then lately with POP3 (for example, webmail with IMAP then download at night with POP3)
and this E-mail comes everytime
anyway to avoid that?