When using AD authentication and sync, only the primary email address gets pulled to Deskpro. The best would be to pull all registered email addresses in AD, to avoid double entries. It is often the case that users have more one or more email aliases (secondary addresses) when you use more than one domain extension (for example .com and .dk). This is for example a problem when forwarding emails into the helpdesk, and manually adding the users email (for example if you have an exchange server that strips the email of internal users). If you accidentally forward with any other email address than the users primary email address, a new user will be created, because Deskpro doesn't know all the users email addresses.