reinject mail: improve error logging

reinject mail: improve error logging

this patch unifies the error handling for mail and rcpt with
the data command: all now die with sensible error (which gets logged
in the error-handling of the eval), and it sets the respose message
and code for those commands as well.

additionally it adds a '\n' to all die statements.

this makes it possible to provide information what went wrong at
call-sites (instead of only having it in syslog)

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by:  Dominik Csapak <d.csapak@proxmox.com>