Please note that some of you are doing assumptions for assignment#1 that do not match the protocol specification. I want to bring your attention to page 4 of RFC 821 where MAIL FROM and RCPT TO commands syntax is shown. Please note there is not a space between the colon and mailbox name. Do not confuse that with what appears inside the message header (From: and To: headers, where a space is found).
Click on the image on the left to get a better view of it.