Step 1:
Once you are ready to set up your email signature, open Postbox. From the top menu, click on Tools and then Options.
Step 2:
From the left menu, select Identity. On the right, select Postbox Signature and click the Edit button next to it.
Step 3:
Delete the default message that is in the text box and paste your email signature into it. Once you are done, click OK.
Step 4:
Your new email signature is now installed! Test it out by composing a new email to make sure it looks correct.