The webmail settings allow you to set a signature for all emails sent from the webmail interface. To do this, log into your email account and follow the steps below.
How-to
First, click the gear icon located in the upper right-hand corner to open your settings.
Next, under the "Mail" section from the menu on the left, select the “Signature” tab.
Here, add the text you’d like to display in the “Signature text” field.
Lastly, click "Save."