Unable to send email using SMTP

We are able to proceed but got some strange message. Able to login retrieve email headers etc.,but not able to send email

Here i am attaching the source code. Here’s the error message:

  1. Sending a simple mail message.

Subject: mail example 6
ERROR: MCSendMail returns Unknown (unexpected).

>>>>>> retrieve mail …
ERROR: MCListMail fails Unknown -21
Done! <<<-----

Thank you