Do you mean allow a user to send with a different account, like from their GMail or Yahoo! account, or another email account on a different domain?

 

If so, then the user can go to SETTINGS > ADVANCED SETTINGS > SMTP ACCOUNTS and click on the [NEW] button to add another SMTP Account that they can send email from using SmarterMail. They would setup SMTP Accounts the same as if they were setting up an email client. They would need to know the SMTP Server Address, Port, Username, Password, and Encryption Type. After using the [TEST CONNECTION] button if the test passes they can click on [SAVE] and from that point onward they can choose to send outgoing mail using that SMTP Account instead of their primary account.