AASTRA DT4x2 for MX-ONE User Guide EN - Manual (Page 84)

Messages
DT412/DT422/DT432 84
To handle the mailbox
Recorded information on the line informs about the number of new
and stored messages. If you have too many messages stored, you
will first be asked to delete saved messages.
Recorded instructions ask you to press different digits in order to
listen to caller's messages, record your own greetings, change
your password or exit your mailbox, etc.
The following diagram gives an overview of the mailbox system and
the digits to be used.
t level