Hi, We are hosting provider (SM Enterpsise12.5) and a client of ours using Apple Mail iCal (Calendar) has problems when tries to add a new task. Doesn't give the option to add attendees or invitees as Apple Mail refers to (see pic prntscr.com/b5ufg8 ).
According to our client this problem doesn't occur with other emails account (e.g gmail or domains hosted to other providers).
Also this problem only occurs to Apple Mail because we tested on Thunderbird 38.7.2 and Outlook 2013 calendars and we can add attendees/invitees without a problem.
I believe this is a compatibility issue and already contacted Apple Customer Support. Their answer is the same : "Seems to be a compatibility issue and should be dealt with the manufacturer since in all other cases working properly"
Before i escalate this issue to Apple, we would like to give us your opinion.