Exchange Online/Office 365 limits for variety of service areas….
You can find the Exchange Online limits for a variety of service areas, including address book limits, Recipient & sender limits, mailbox storage limits, reporting, message trace limits, mailbox folder limits, retention limits and more. You can refer the detailed information @ https://technet.microsoft.com/en-in/library/exchange-online-limits.aspx. For limits that apply to EOP features in Exchange Online, you can refer Exchange Online Protection Limits.
Hope this helps.