Just quick reminder about attributes which are synced to AAD. I have been searching once again this information at current project due the problems with sync engines.

DirSync

List of attributes that are synced by the Azure Active Directory Sync Tool

Link contains following tables

Table 1: Attributes that are synced from the on-premises Active Directory Domain Services (AD DS) to Windows Azure Active Directory (Windows Azure AD

Table 2: Attributes that are written back to the on-premises AD DS from Windows Azure Active Directory in an Exchange hybrid deployment scenario

And interesting part “How directory synchronization determines what isn’t synced from the on-premises environment to Windows Azure AD”

AAD Sync

AAD Sync – Attributes synchronized to Azure Active Directory

AAD Connect

Base documentation for AAD Connect