May be related to 8.52 fix for spr TTAN7P7QG6. That problem was internet address from contact marked as "other internet mail" should not be converted back to Notes address

HCL Notes/Domino 8.5 Forum (includes Notes Traveler)

Subject:

Normally in Notes if the internet address can be found as a Notes address, than we use the Notes address to prevent unnecessary mime conversion. This was broken in 8.0, and fixed in 8.51. In 8.52 we added the check to make sure the MailSystem was set to Notes before converting back.

You can prevent the address conversion from happening by setting Notes.ini "TYPEDOWN_LEAVE_AS_SMTP=1"

Feedback response number RRAL89WLWW created by ~Chris Zenkrotherynds on 10/04/2010