Auto detection of external/internal attendees.
Default the attendee type to "External".
When the name is entered from the internal address book, then it will change to "Internal".
In Outlook Add-in, based on the "To:" list, do a detection if attendees are Internal or External, based on email address.
This will ease the need to tagging attendees to "External" to register them into the Visitor Management System.

We’re happy to tell you that this feature is now available in our latest Outlook Add-in release, 6.6.4 in conjunction with our Enterprise 23 August update.
Thanks for voting on the idea.
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Teo Chin Keong commented
When the user enter a different email domain, other than the same organization, the system should understand that the attendees is from "External", without the need to change the Type