A recipient is any email address listed in the To, Cc or Bcc headers of the email, or specified via SMTP commands.
While the default limits are ample for most users, we realize that some of our customers might have a legitimate requirement to send larger volumes of mail. We're more than happy to raise the limits to whatever works for you (so long as your use of our SMTP servers complies with our acceptable use policy, essentially: no spam).
For more information about raising your send limit, see the next question.
There's also a total monthly bandwidth limit for each type of account. If your total bandwidth usage exceeds the limit, you will need to purchase additional bandwidth at the rate of $10 per GB. You can check your bandwidth usage from the "My Neo" section of the site.