Description
Use this option to select whether to apply the sender's personal signature or the mailbox signature by default when sending an email from a mailbox that is not the user's own in the Outlook Add-in, such as a shared mailbox or when sending on behalf of another user.
NOTE: The Default Signature Source feature works independently of Send on Behalf. Enabling or disabling Send on Behalf does not affect the Default Signature Source setting.
How to access it
To access the Default Signature Source option:
- From the header bar, select the cogwheel icon, then select Mail Flow.
- Navigate to the Default Signature Source section.

The Default Signature Source section.
Configuring Default Signature Source
To select which signature is applied by default when sending from a mailbox that is not the user's own in the Outlook Add-in:
- Either:
- Select Sender's own signature to apply the signed-in user's signature by default.
- Select Mailbox signature to apply the signature assigned to the mailbox in the From address by default.
- Select Save.