Problem with active Sync

[jbeunel]

Hello
We have a problem with Active sync on Iphone 5 and 6 only, everything works fine with iphones 4.
Email arrive with the date 1970 and we can't open them, we have to close Mail and try again.
A lot of contacts are missing, and when we open contact it freeze very often.
When we refresh email we receive the last email 3 , 4 , 5 time the same email.
Do you have any ideas?
We use Zimbra 8.6.0 patch 4.
I don't know if it's a problem since IOS 9.0.2 or since we have updated our Zimbra to 8.6.0.
Regards