Emails with sender MISSING_MAILBOX at missing_domain

[grupo correo]

Hello,

we are working in the migration from courier-imap to dovecot
2.2.10-4.el7_0.1.x86_64.

Some emails that send a internal application show as sender
"MISSING_MAILBOX at missing_domain", i use like email client  Horde using
dovecot like server. But if i open that email with Horde and courier-imap i
can see the correct email sender.

I think that the email of the sender is no correct or not accomplish some
RFC. Can anyone help me to understand this?

Thank you