Google has started requiring incoming mail to comply with more of RFC2822, particularly with respect to headers; to wit they won't accept incoming mail without a "From:" header. If you try to send without on, you'll get a rejection like this:
this message is not RFC 2822 compliant. To reduce the amount of spam 5.7.1 sent to Gmail, this message has been blocked. Please review 5.7.1 RFC 2822 specifications for more information. iw4si27447595pac.153 - gsmtp
This isn't an issue when you use a mail client, but if you're manually entering SMTP commands, it adds an extra requirement. The following is a conforming session, or at least conforming enough -- the RFC requires a Date header as well, but Google isn't enforcing that
$ telnet smtp-server 25
220 SMTP_SERVER Microsoft ESMTP MAIL Service ready at Thu, 27 Jun 2013 22:45:15 -0400
helo
250 SMTP_SERVER Hello [10.103.13.44]
mail from: my_address@domain
250 2.1.0 Sender OK
rcpt to: target_address@domain.gmail.com
250 2.1.5 Recipient OK
data
354 Start mail input; end with <CRLF>.<CRLF>
From: ME
Subject: testing SMTP
this is a test
(props to)
A
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