Connecting to smtp.gmail.com via command line

问题:

I am in the process of writing an application that sends mail via an valid GMail user ID and password.

I just wanted to simulate the SMTP connection on my Windows XP command line, and when I telnet smtp.gmail.com at 465 port - I don't see any thing. A blank command window with title Telnet smtp.gmail.com opens with cursor. When I type in EHLO or usual SMTP handshake commands, the prompt just closes.

I am unable to figure out whats going wrong and where. I tried connecting to 587, it does not connect in telnet at all. Could anyone please clarify if I am doing something wrong?

回答1:

Using Linux or OSx, do what Sorin recommended but use port 465 instead. 25 is the generic SMTP port, but not what GMail uses. Also, I don't believe you want to use -starttls smtp

openssl s_client -connect smtp.gmail.com:465

You should get lots of information on the SSL session and the response:

220 mx.google.com ...

Type in

HELO smtp.gmail.com 

and you'll receive:

250 mx.google.com at your service

From there it is not quite as straightforward as just sending SMTP messages because Gmail has protections in place to ensure you only send emails appearing to be from accounts that actually belong to you. Instead of typing in "Helo", use "Ehlo". I don't know much about SMTP so I cannot explain the difference, and don't have time to research much. Perhaps someone with more knowledge can explain.

Then, type "auth login" and you will receive the following:

334 VXNlcm5hbWU6

This is essentially the word "Username" encoded in Base 64. Using a Base 64 encoder such as this one, encode your user name and enter it. Do the same for your password, which is requested next. You should see:

235 2.7.0 Accepted

And that's it, you're logged in.

There is one more oddity to overcome if you're using OSx or Linux terminals. Just pressing the "ENTER" key does not apparently result in a CRLF which SMTP needs to end a message. You have to use "CTRL+V+ENTER". So, this should look like the following:

^M
.^M
250 2.0.0 OK

回答2:

For OSX' terminal:

openssl s_client -connect smtp.gmail.com:25 -starttls smtp 

回答3:

Gmail require SMTP communication with their server to be encrypted. Although you're opening up a connection to Gmail's server on port 465, unfortunately you won't be able to communicate with it in plaintext as Gmail require you to use STARTTLS/SSL encryption for the connection.

回答4:

Jadaaih, you can connect send SMTP through CURL - link to Curl Developer Community.

This is Curl Email Client source.

回答5:

Try this:

telnet smtp.gmail.com 587

回答6:

Check this post in lifehacker : Geek to Live: Back up Gmail with fetchmail . It uses a command line program. Check and see if it helps. BTW why are you using command line when there are many other nice alternatives?

回答7:

tcp/465 was initially intended for establishing the SSL(and newer TLS) layer first, and inside doing cleartext or plain old protocols (smtp here)

tcp/587 was intended as a replacement to default tcp/25 port initially when spammers and mass mailing attacks commenced like a decade or more ago, but also during those infamous AOL ages, when some funny ISP had some blocks on default ports outbound (such as that tcp/25) for denying their own customers (AOL) to mass-send emails/spam back then, but AOL-customers needing to use alternative mail-accounts and mail-providers still needed to send their mails from AOL-internet connections, so they could still connect to tcp/587 and do simple smtp on it back then.

The deal with the STARTTLS way to do smtp is to use the two well known originally plain-text tcp/25 and tcp/587 ports, and only when the initial clear-text connect suceeded, to then START the TLS layer (thus STARTTLS) from there on, having a secured connection from that point onwards.

As for debugging these kind of things maybe via command-line tools, for example for windows there is the historical blat command line mailer (smtp), which up till today cant do TLS (STARTTLS) so it can only use plain-text smtp to send its mails.

http://www.blat.net/

Then there are numerous projects freeware and open source software that have more capabilities and features, such as

smtp client: mailsend @ googlecode http://code.google.com/p/mailsend/

smtp client: msmtp @ sourceforge (related to mpop below) http://msmtp.sourceforge.net/

pop3 client: mpop @ sourceforge http://mpop.sourceforge.net/

回答8:

Start session from terminal:

openssl s_client -connect smtp.gmail.com:25 -starttls smtp

The last line of the response should be "250 SMTPUTF8"

Initiate login

auth login

This should return "334 VXNlcm5hbWU6".

Type username

Type your username in base64 encoding (eg. echo -n 'your-username' | base64)

This should return "334 UGFzc3dvcmQ6"

Type password

Type your password in base64 encoding (eg. echo -n 'your-password' | base64)

Success

You should see "235 2.7.0 Accepted" and you're are successfully logged in

回答9:

gmail uses an encrypted connection. So, even after you establish a connection, you wont be able to send any email. The encryption is a little complex to manage. Try using openssl instead.

The thread below should help-

How to send email using simple SMTP commands via Gmail?