When you share a map, email notification is sent to your colleague with a link to register for Mapline and view your map. If the notification email was never received, it could caused by two reasons:
If this happens, check the email address you shared the map with. Also, ask your colleague to check their SPAM or JUNK folder.
If neither of these prove successful, then tell your colleague to register for Mapline using the same email address as the one you shared your map with. Once they register, they will see your map available to them when they login.