Recently was asked for supported configurations for server side sync for CRM 2015 online. Here is the matrix:
CRM deployment |
Email system |
Email synchronization |
Appointments, contacts, and tasks synchronization |
Protocol |
CRM (on-premises) |
|
Yes |
Yes |
Exchange Web Services |
CRM (on-premises) |
|
Yes |
No |
POP3/SMTP |
Microsoft Dynamics CRM Online |
Exchange Online |
Yes |
Yes |
Exchange Web Services |
Microsoft Dynamics CRM Online |
|
Yes |
No |
POP3/SMTP |
Source: Technet
Hope it helps!