I use Mac Mail as my email client and Mac Calendar. The calendar is synced to my Google calendar. My work email is received via an imap connection to an old Exchange server. When I receive an invite I click on it and open it in Calendar, accept it, and then it is automatically syncd with Google and turns grey. I think this is because I have accepted it from my Gmail account, as when I look at the list of recipients my work email address is flagged as unknown, while my Gmail account is listed as accepted. Is there any way to accept invites through Mac Mail using Calendar and still have them sync with my Google Calendar, and so not appear as greyed items?