Custom attributes are not populated in hybrid environment

Problem

You are in a hybrid environment and custom attributes for users are not populated in Signature 365.

Reason

Custom attributes are not being synchronised from your on-premise Active Directory to Azure AD.

Solution

Completing the steps below will ensure custom attributes are synchronised from Active Directory to Azure AD:

1. Open Microsoft Azure Active Directory Connect
2. On the Optional Features pane, tick the Directory extension attribute sync option:
   
   
3. On the Directory Extensions pane, add extensionAttribute1 (user) through to extensionAttribute15 (user) to Selected Attributes:
   
   
4. Complete the wizard