Feature Request: notification for invalid password

[sebo505]

First of all, mailnag is really great, exactly what I was looking for. The only downside: ocasionally I change my mail password for security reasons. It happens that I then forget to provide mailnag with the new password. This I might notice days or weeks later, cause mailnag just quietly stops working since it still uses the old and now invalid mail password and thus does not report any new mails. In my opinion it would be desirable if mailnag came up with a notification/error message in this case to remind the user to update the mail-password in mailnag.