getting “530 5.7.0 Must issue a STARTTLS command first.” error when sending mail via netcat

问题

I'm trying to send an email with netcat, this is what i get:

****-MacBook-Pro:~ ***$ nc smtp.gmail.com 25
220 mx.google.com ESMTP h8sm66301168eew.16 - gsmtp
Helo gmail.com
250 mx.google.com at your service
MAIL FROM: <******@gmail.com>
530 5.7.0 Must issue a STARTTLS command first. h8sm66301168eew.16 - gsmtp

what is STARTTLS command and what do i need to do with it?

回答1:

STARTTLS is an extension to plain text communication protocols, which offers a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead of using a separate port for encrypted communication.

http://en.wikipedia.org/wiki/STARTTLS

The smtp server is saying it won't accept plain text connections.

回答2:

You basicaly just need to specify that you're using TLS.

回答3:

Use EHLO instead of HELO. This will start 250-STARTTLS.

来源：https://stackoverflow.com/questions/19914036/getting-530-5-7-0-must-issue-a-starttls-command-first-error-when-sending-mail