Smartermail has a "mailbox migration tool" which makes easy switching from your previous email provider to Smartermail; it allows to import email, contacts, calendars, tasks, and notes to SmarterMail from most third-party mail servers.

To access the mailbox migration tool, on Smartemail's webmail click the settings icon. Then expand the My Settings and Advanced Settings folders and click Mailbox Migration. The mailbox migration tool will open in a new window.

Follow the on-screen instructions to import email and collaboration data from a third-party mail server to your SmarterMail mailbox.
Depending on the mail server you are migrating from, you may be asked to provide the mailbox protocol (POP, IMAP), the server address, port, username and password. 

It may take a long time for your mailbox data to import. You can continue using SmarterMail during this time as the migration process happens in the background. In addition, the type of items available for migration are purely dependent upon the service you're migrating from. SmarterMail can not migrate any item that is not allowed by the service provider.