By default, manual signature selection is disabled in the Outlook add-in. Signatures are automatically applied according to the context.
Go to Settings
Click on Connectors
Select your Outlook Add-in Connector
Scroll down to the Signature selection management

Check Enable manual selection
Save your changes if necessary
Once activated:
Users will be able to manually choose their signature
The option will be available when composing an email
This applies to new messages and replies, both internally and externally

If the option is deactivated, the signature is automatically applied according to the rules defined in Signitic. The automation remains active, even if the option is enabled.