This may just be the way the plugin is designed to work.If I'm reading this correctly, In the plugin settings, your Default Domain: is set to 'domain.org'?Some of your users have email addresses @ 'domain2.org', and those don't work.Have you tried any of the users who's emails are @ domain.org?I have a similar situation--my Default Domain is 1stDomain.com. All of my users can use either 1stDomain.com or 2ndDomain.com as their email address. However, if they are logging into (or being assigned a ticket in) osTicket, only 1stDomain.com is recognized. The user lookup seems to only look in whatever domain is in the "Default Domain" setting.