telnet 500 Syntax error, command unrecognized

Question

I'm trying to send email using telnet in cmd. I have connection with telnet now

C:\Users\Student>telnet alt3.gmail-smtp-in.l.google.com 25

then it brought me here:

220 mx.google.com ESMTP c8si3296343qgc.94 - gsmtp

I then type helo to make sure I'm connected which I should get a 250

ehlo
250-mx.google.com at your service, [103.16.169.202]
250 SIZE 35882577

The next command after receiving the 250 should be:

mail from: <cedr******@gmail.com>

which brought me to

500 Syntax error, command unrecognized

I've read several sites which says that firewalls must be compliant with section 3.1.2 of RFC 2979 (Firewall Requirements) and I should make sure that the firewall is not disabling any SMTP function your server requires, such as SMTP Authentication. If my firewall has a "Proxy" for SMTP, I should remove it and then add my own that does nothing with Port 25.

So can please someone tell me how can I do that. I'm totally not aware where to find those things, or if you have alternatives please tell me so. Thanks!

Answer 1

The SMTP RFC says:

Since it has been a common source of errors, it is worth noting that spaces are not permitted on either side of the colon following FROM in the MAIL command or TO in the RCPT command.

Earlier versions of the RFC didn't explicitly disallow it, but they never explicitly allowed it either and all the examples in the RFCs were always without spaces. Somehow the space after the colon became accepted by a lot of servers and used by a lot of clients in spite of being unjustifiable by anything in the specification.