If you've connected your Microsoft Exchange or Office 365 email account and you're getting a "Cannot send mail" error, try these steps to enable LeadSimple to send on your behalf.
Login into Outlook email (through web browser)
Under Settings > IMAP and POP > Check box for "Let devices and apps use POP"
That should fix the problem! If not, see here for more details, and let us know if you're still having trouble.