A welcome message is an optional email that you can choose to send to new subscribers upon sign up (if your list is a single opt-in or once they have confirmed their email address (if your list is a double or confirmed opt-in).
To set up and edit your welcome email, access your contact list and click on Manage Emails on the left hand menu.
Under Welcome Email you will see the option to preview and edit both HTML and text versions of the email, send a test, and active/deactivate it. Feel free to customize it any way you want!
Note: Welcome emails cannot be edited within a trial account.