要通过 gmail 发送，您需要使用加密连接。单独使用 telnet 是不可能的，但您可以使用openssl 之类的工具
使用openssl 中的 starttls 选项进行连接，将普通连接转换为加密连接...
openssl s_client -starttls smtp -connect smtp.gmail.com:587 -crlf -ign_eof
或直接连接到 ssl 套接字...
openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof
EHLO 本地主机
之后，使用 base64 编码的用户名/密码对服务器进行身份验证
AUTH 普通 AG15ZW1haWxAZ21haWwuY29tAG15cGFzc3dvcmQ=
从命令行获取：
echo -ne '\00user@gmail.com\00password' | base64
AHVzZXJAZ21haWwuY29tAHBhc3N3b3Jk
然后继续“来自：”的邮件，就像你的例子一样
示例会话：
openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof
[... lots of openssl output ...]
220 mx.google.com ESMTP m46sm11546481eeh.9
EHLO localhost
250-mx.google.com at your service, [1.2.3.4]
250-SIZE 35882577
250-8BITMIME
250-AUTH LOGIN PLAIN XOAUTH
250 ENHANCEDSTATUSCODES
AUTH PLAIN AG5pY2UudHJ5QGdtYWlsLmNvbQBub2l0c25vdG15cGFzc3dvcmQ=
235 2.7.0 Accepted
MAIL FROM: <gryphius-demo@gmail.com>
250 2.1.0 OK m46sm11546481eeh.9
rcpt to: <somepoorguy@example.com>
250 2.1.5 OK m46sm11546481eeh.9
DATA
354 Go ahead m46sm11546481eeh.9
Subject: it works
yay!
.
250 2.0.0 OK 1339757532 m46sm11546481eeh.9
quit
221 2.0.0 closing connection m46sm11546481eeh.9
read:errno=0
正如没有人提到的那样-我建议为此目的使用出色的工具-swaks
# yum info swaks
Installed Packages
Name : swaks
Arch : noarch
Version : 20130209.0
Release : 3.el6
Size : 287 k
Repo : installed
From repo : epel
Summary : Command-line SMTP transaction tester
URL : http://www.jetmore.org/john/code/swaks
License : GPLv2+
Description : Swiss Army Knife SMTP: A command line SMTP tester. Swaks can test
: various aspects of your SMTP server, including TLS and AUTH.
它有很多选择，几乎可以做任何你想做的事情。
GMAIL：STARTTLS、SSLv3（是的，在 2016 年 gmail 仍然支持 sslv3）
$ echo "Hello world" | swaks -4 --server smtp.gmail.com:587 --from user@gmail.com --to user@example.net -tls --tls-protocol sslv3 --auth PLAIN --auth-user user@gmail.com --auth-password 7654321 --h-Subject "Test message" --body -
=== Trying smtp.gmail.com:587...
=== Connected to smtp.gmail.com.
<- 220 smtp.gmail.com ESMTP h8sm76342lbd.48 - gsmtp
-> EHLO www.example.net
<- 250-smtp.gmail.com at your service, [193.243.156.26]
<- 250-SIZE 35882577
<- 250-8BITMIME
<- 250-STARTTLS
<- 250-ENHANCEDSTATUSCODES
<- 250-PIPELINING
<- 250-CHUNKING
<- 250 SMTPUTF8
-> STARTTLS
<- 220 2.0.0 Ready to start TLS
=== TLS started with cipher SSLv3:RC4-SHA:128
=== TLS no local certificate set
=== TLS peer DN="/C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com"
~> EHLO www.example.net
<~ 250-smtp.gmail.com at your service, [193.243.156.26]
<~ 250-SIZE 35882577
<~ 250-8BITMIME
<~ 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
<~ 250-ENHANCEDSTATUSCODES
<~ 250-PIPELINING
<~ 250-CHUNKING
<~ 250 SMTPUTF8
~> AUTH PLAIN AGFhQxsZXguaGhMGdATGV4X2hoYtYWlsLmNvbQBS9TU1MjQ=
<~ 235 2.7.0 Accepted
~> MAIL FROM:<user@gmail.com>
<~ 250 2.1.0 OK h8sm76342lbd.48 - gsmtp
~> RCPT TO:<user@example.net>
<~ 250 2.1.5 OK h8sm76342lbd.48 - gsmtp
~> DATA
<~ 354 Go ahead h8sm76342lbd.48 - gsmtp
~> Date: Wed, 17 Feb 2016 09:49:03 +0000
~> To: user@example.net
~> From: user@gmail.com
~> Subject: Test message
~> X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
~>
~> Hello world
~>
~>
~> .
<~ 250 2.0.0 OK 1455702544 h8sm76342lbd.48 - gsmtp
~> QUIT
<~ 221 2.0.0 closing connection h8sm76342lbd.48 - gsmtp
=== Connection closed with remote host.
雅虎：TLS 又名 SMTPS，tlsv1.2
$ echo "Hello world" | swaks -4 --server smtp.mail.yahoo.com:465 --from user@yahoo.com --to user@gmail.com --tlsc --tls-protocol tlsv1_2 --auth PLAIN --auth-user user@yahoo.com --auth-password 7654321 --h-Subject "Test message" --body -
=== Trying smtp.mail.yahoo.com:465...
=== Connected to smtp.mail.yahoo.com.
=== TLS started with cipher TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128
=== TLS no local certificate set
=== TLS peer DN="/C=US/ST=California/L=Sunnyvale/O=Yahoo Inc./OU=Information Technology/CN=smtp.mail.yahoo.com"
<~ 220 smtp.mail.yahoo.com ESMTP ready
~> EHLO www.example.net
<~ 250-smtp.mail.yahoo.com
<~ 250-PIPELINING
<~ 250-SIZE 41697280
<~ 250-8 BITMIME
<~ 250 AUTH PLAIN LOGIN XOAUTH2 XYMCOOKIE
~> AUTH PLAIN AGFhQxsZXguaGhMGdATGV4X2hoYtYWlsLmNvbQBS9TU1MjQ=
<~ 235 2.0.0 OK
~> MAIL FROM:<user@yahoo.com>
<~ 250 OK , completed
~> RCPT TO:<user@gmail.com>
<~ 250 OK , completed
~> DATA
<~ 354 Start Mail. End with CRLF.CRLF
~> Date: Wed, 17 Feb 2016 10:08:28 +0000
~> To: user@gmail.com
~> From: user@yahoo.com
~> Subject: Test message
~> X-Mailer: swaks v20130209.0 jetmore.org/john/code/swaks/
~>
~> Hello world
~>
~>
~> .
<~ 250 OK , completed
~> QUIT
<~ 221 Service Closing transmission
=== Connection closed with remote host.
在过去的 5 年里，我一直在使用 swaks 通过 gmail 从 nagios 发送电子邮件通知，没有任何问题。
根据现有的答案，这里有一个分步指南，通过 SMTP 发送自动电子邮件，使用 GMail 帐户，从命令行，不透露密码。
首先，安装以下软件包：
这些说明假定为 Linux 操作系统，但应该很容易移植到 Windows（通过 Cygwin 或本机等效程序）或其他操作系统。
将以下 shell 脚本另存为authentication.sh：
#!/bin/bash
# Asks for a username and password, then spits out the encoded value for
# use with authentication against SMTP servers.
echo -n "Email (shown): "
read email
echo -n "Password (hidden): "
read -s password
echo
TEXT="\0$email\0$password"
echo -ne $TEXT | base64
使其可执行并按如下方式运行：
chmod +x authentication.sh
./authentication.sh
出现提示时，提供您的电子邮件地址和密码。这看起来像：
Email (shown): bob@gmail.com
Password (hidden):
AGJvYkBnbWFpbC5jb20AYm9iaXN0aGViZXN0cGVyc29uZXZlcg==
复制最后一行 ( AGJ...==)，因为这将用于身份验证。
将以下期望脚本另存为notify.sh（注意第一行指的是期望程序）：
#!/usr/bin/expect
set address "[lindex $argv 0]"
set subject "[lindex $argv 1]"
set ts_date "[lindex $argv 2]"
set ts_time "[lindex $argv 3]"
set timeout 10
spawn openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof
expect "220" {
send "EHLO localhost\n"
expect "250" {
send "AUTH PLAIN YOUR_AUTHENTICATION_CODE\n"
expect "235" {
send "MAIL FROM: <YOUR_EMAIL_ADDRESS>\n"
expect "250" {
send "RCPT TO: <$address>\n"
expect "250" {
send "DATA\n"
expect "354" {
send "Subject: $subject\n\n"
send "Email sent on $ts_date at $ts_time.\n"
send "\n.\n"
expect "250" {
send "quit\n"
}
}
}
}
}
}
}
进行以下更改：
YOUR_AUTHENTICATION_CODE身份验证脚本生成的身份验证代码。YOUR_EMAIL_ADDRESS用于生成验证码的电子邮件地址。例如（注意电子邮件地址保留了尖括号）：
send "AUTH PLAIN AGJvYkBnbWFpbC5jb20AYm9iaXN0aGViZXN0cGVyc29uZXZlcg==\n"
send "MAIL FROM: <bob@gmail.com>\n"
最后，使通知脚本可执行如下：
chmod +x notify.sh
从命令行发送电子邮件，如下所示：
./notify.sh recipient@domain.com "Command Line" "March 14" "15:52"