New error reason: Send More Slowly

[azumakuniyuki]

• error messages:
  • 450-4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered
  • 421-4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address.
  • 452 4.3.2 Connection rate limit exceeded.
• reason name
  • sendslowly
  • ratelimited

[azumakuniyuki]

#465 toomanyconn will be changed to sendslowly OR ratelimited.