Some messages may be hidden. By default these are not displayed in Message list. When some messages are hidden, a button Show hidden appears in command bar, which allows you to reveal hidden messages.
Purpose of hiding messages
The idea behind hiding is to filter out messages that you don’t want to reply or further care of on your mobile device. Yet you also do not want to delete the message. Possibly hidden messages will be dealt with on your PC, or you may come to them later.
Synchronization with mail server
ProfiMail synchronizes hidden flag with IMAP server (if server supports custom message flags). But message hiding is not standard functionality, so other email clients won’t recognize that messages are hidden.
Synchronization of hidden flag is useful if you use ProfiMail on more devices. Then hiding message on one device will make it hidden on another device (in ProfiMail).