To import new leads into LeadSimple automatically, you'll need a LeadSimple email address. The lead source you'd like to import new leads from will simply need to CC leads to that email address and LeadSimple will create them in your account.
These email addresses are generated by creating a lead source. (under Settings > Sources > Add Source).
Name your lead source after the marketing channel leads will be coming from and make sure "Automatically import leads via email" is selected.
Next, copy the Forwarding Address in the dialog window that appears. This is the email address you'll need to give your lead provider to send emails to. You can also enter an email to send instructions to your webmaster.