SMTP
SMTP—简单邮件传输协议，是用来发送邮件的，不是用来接受邮件的。从RFC发布历程中，SMTP 是个生命力顽强的协议;
- 1981 RFC788 SMTP 正式发布 第一个版本
- 1995 RFC1869 SMTP 扩展版本协议发布(ESMTP), 引入登陆认证机制，MIME支持多媒体，SSL/TLS 安全之类的
现代主流的SMTP 其实都是 ESMTP，这不重要啦，因为大家都一样，一个代称而已; SMTP 协议是一种问答式协议， 有点像问答题，问一句答一句； 所以SMTP 定义 一套类似 语文中 ”主谓宾" 语法；
| 指令 | 含义 | 示例 |
|---|---|---|
| EHLO | 客户端发起邮件申请，并查询服务端 支持的扩展列表 | ehlo localhost |
| 设置邮件发件人 | mail from:sender@email.comsender@email.com | |
| RCPT | 设置邮件收件人 | rcpt to:receive@email.comreceive@email.com |
| DATA | 发送邮件内容主体 | 注意编码 和 结束符号. |
SMTP支持指定编码方式 例如 utf8, gbk 等，其中 B表示Base64 编码
抓包分析
- TCP 建立连接 3次握手
- 客户端 ehlo ，服务端返回支持列表
- 客户端认证， 明文传输
- 构造邮件报文
Telnet 交互式发送邮件
Telnet连接QQ邮件服务器，发送一封包含附件的邮件。 邮件内容如下：
- Telnet 连接 QQ邮件服务器，QQ邮件服务器分企业邮件服务器(smtp.exmail.qq.com) 和普通邮件服务器(smtp.qq.com), 并开始ehlo 命令
$ telnet smtp.exmail.qq.com 25
Trying 157.148.36.163...
Connected to smtp-v6.exmail.qq.com.
Escape character is '^]'.
220 smtp.qq.com Esmtp QQ QMail Server
ehlo richard
250-smtp.qq.com
250-PIPELINING
250-SIZE 73400320
250-STARTTLS
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN
250-MAILCOMPRESS
250 8BITMIME
链接上QQ邮件服务器之后， ehlo 可以随意设置, 然后QQ邮件服务器会返回 它支持的邮件扩展能力
- 登陆认证QQ邮件服务器， 需要输入用户和密码， 对于企业邮箱用户和密码， 对于非企业邮箱用户 需要用户名和授权码; 编码是Base64
auth login
334 VXNlcm5hbWU6 // base64 反序列化 Username:
6L6T5YWl6Ieq5bex55qE55So5oi35ZCN
334 UGFzc3dvcmQ6 // base64 发序列化 Password:
6L6T5YWl6Ieq5bex55qE5a+G56CB
235 Authentication successful
输入正确后， QQ邮件服务器会返回 认证成功 的信息
- 设置发送邮件的发件人，收件人和邮件信息
mail from:<sender@email.com>sender@email.com size=16384 //设置发件人
250 Ok
rcpt to:<receive@email.com> //设置收件人
250 Ok
data //设置邮件内容， 最后以 . 结束
354 End data with <CR><LF>.<CR><LF>
- 设置邮件内容主题
From: sender@email.com // 需要和mail 命令指定的一致
To: receive@email.com // 需要和rcpt 命令指定的一致
Subject: =?UTF8?B?5r+A5rS76LSm5Y+36YCa55+l6YKu5Lu25o+Q6YaS?=
MIME-Version: 1.0
X-Business-Group: YSZX-CN
Content-Type: multipart/mixed;
boundary="----=_Part_690a405a-d366-48f4-a760-48433c5237d5"
------=_Part_690a405a-d366-48f4-a760-48433c5237d5
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: base64
CkRlYXIgS2VsbHkKCiAgICDov5nmmK/kuIDlsIHmv4DmtLvpgq7ku7bmj5DphpLvvIwg5aaC5p6c5rKh5pyJ5r+A5rS76K+354K55Ye75Lul5LiL6ZO+5o6lCiAgICAKICAgIGh0dHBzOi8vcmljaGFyZC5wdWIvCgoKQmVzdApSaWNoYXJkCg==
------=_Part_690a405a-d366-48f4-a760-48433c5237d5
Content-Type: application/octet-stream; name="=?UTF-8?B?5rWL6K+V6ZmE5Lu25paH5Lu2Lmh0bWw=?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="=?UTF-8?B?5rWL6K+V6ZmE5Lu25paH5Lu2Lmh0bWw=?="
CkRlYXIgS2VsbHkKCiAgICDov5nmmK/kuIDlsIHmv4DmtLvpgq7ku7bmj5DphpLvvIwg5aaC5p6c5rKh5pyJ5r+A5rS76K+354K55Ye75Lul5LiL6ZO+5o6lCiAgICAKICAgIGh0dHBzOi8vcmljaGFyZC5wdWIvCgoKQmVzdApSaWNoYXJkCg==
------=_Part_690a405a-d366-48f4-a760-48433c5237d5--
.
250 Ok: queued as
OpenSSL 交互式发送邮件
- openssl client 连接QQ邮件服务器
$ openssl s_client -crlf -connect smtp.exmail.qq.com:465
CONNECTED(00000006)
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root CA
verify return:1
depth=1 C = US, O = DigiCert Inc, CN = DigiCert Secure Site CN CA G3
verify return:1
depth=0 C = CN, ST = Guangdong Province, L = Shenzhen, O = Tencent Technology (Shenzhen) Company Limited, CN = *.exmail.qq.com
verify return:1
---
Certificate chain
0 s:/C=CN/ST=Guangdong Province/L=Shenzhen/O=Tencent Technology (Shenzhen) Company Limited/CN=*.exmail.qq.com
i:/C=US/O=DigiCert Inc/CN=DigiCert Secure Site CN CA G3
1 s:/C=US/O=DigiCert Inc/CN=DigiCert Secure Site CN CA G3
i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert Global Root CA
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=CN/ST=Guangdong Province/L=Shenzhen/O=Tencent Technology (Shenzhen) Company Limited/CN=*.exmail.qq.com
issuer=/C=US/O=DigiCert Inc/CN=DigiCert Secure Site CN CA G3
---
No client certificate CA names sent
Server Temp Key: ECDH, X25519, 253 bits
---
SSL handshake has read 3618 bytes and written 289 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES128-GCM-SHA256
Session-ID: 3AC1D8BE26892228A8AB4F98BD532B671A9D7563A703DF029C8AA650ED620892
Session-ID-ctx:
Master-Key: BDE43DADEE9CB47631D38F33A005918A210057C8F1B85405285ED7406DCEBAB1F8D9456DBF848EEF3C7B0A5F60ED7608
TLS session ticket lifetime hint: 1200 (seconds)
TLS session ticket:
0000 - c8 0b e5 63 d4 a4 32 15-f8 b8 67 21 69 3a 46 3a ...c..2...g!i:F:
0010 - b4 62 74 9e f2 15 17 fd-6f 87 ad 64 31 69 28 cd .bt.....o..d1i(.
0020 - a1 66 6d 53 c3 99 e0 1b-97 75 88 b8 91 bb 6a 05 .fmS.....u....j.
0030 - 89 c5 36 53 4b da 54 f9-57 af 74 a3 6c 34 79 ef ..6SK.T.W.t.l4y.
0040 - a3 e5 28 6f 86 17 cf ab-b8 c1 3d c0 b0 e8 59 03 ..(o......=...Y.
0050 - 63 f7 a7 f4 92 75 62 70-17 77 0e a7 15 82 8e b0 c....ubp.w......
0060 - f2 26 d4 1b 89 60 54 bf-d9 1a 0f 4b 85 66 69 ac .&...`T....K.fi.
0070 - af cd 43 ef ed 4c a3 13-fe 6d 44 c9 ba 9e 45 d8 ..C..L...mD...E.
0080 - 7e ec 03 b9 44 0f c2 ff-d2 50 e8 d7 9a 3e 41 93 ~...D....P...>A.
0090 - ab 26 46 c8 75 7a b3 d8-64 ae 48 c7 76 db 5c 97 .&F.uz..d.H.v.\.
00a0 - e3 55 0d 7a 7f 3f 1a e2-94 dc 7f ba d2 f1 65 15 .U.z.?........e.
Start Time: 1661145639
Timeout : 7200 (sec)
Verify return code: 0 (ok)
---
220 smtp.qq.com Esmtp QQ QMail Server
- 查看QQ邮件服务器扩展
ehlo richard
250-smtp.qq.com
250-PIPELINING
250-SIZE 73400320
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN
250-MAILCOMPRESS
250 8BITMIME
- QQ邮件服务器认证
auth login
334 VXNlcm5hbWU6 // base64 反序列化 Username:
6L6T5YWl6Ieq5bex55qE55So5oi35ZCN
334 UGFzc3dvcmQ6 // base64 发序列化 Password:
6L6T5YWl6Ieq5bex55qE5a+G56CB
235 Authentication successful
- 设置发件人和收件人
mail from:<sender@email.com>sender@email.com
250 Ok
rcpt to:<receive@email.com>
250 Ok
- 发送邮件内容
data
354 End data with <CR><LF>.<CR><LF>
From: sender@email.com
To: receive@email.com
Subject: =?UTF8?B?5r+A5rS76LSm5Y+36YCa55+l6YKu5Lu25o+Q6YaS?=
MIME-Version: 1.0
X-Business-Group: YSZX-CN
Content-Type: multipart/mixed;
boundary="----=_Part_690a405a-d366-48f4-a760-48433c5237d5"
------=_Part_690a405a-d366-48f4-a760-48433c5237d5
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: base64
CkRlYXIgS2VsbHkKCiAgICDov5nmmK/kuIDlsIHmv4DmtLvpgq7ku7bmj5DphpLvvIwg5aaC5p6c5rKh5pyJ5r+A5rS76K+354K55Ye75Lul5LiL6ZO+5o6lCiAgICAKICAgIGh0dHBzOi8vcmljaGFyZC5wdWIvCgoKQmVzdApSaWNoYXJkCg==
------=_Part_690a405a-d366-48f4-a760-48433c5237d5
Content-Type: application/octet-stream; name="=?UTF-8?B?5rWL6K+V6ZmE5Lu25paH5Lu2Lmh0bWw=?="
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="=?UTF-8?B?5rWL6K+V6ZmE5Lu25paH5Lu2Lmh0bWw=?="
CkRlYXIgS2VsbHkKCiAgICDov5nmmK/kuIDlsIHmv4DmtLvpgq7ku7bmj5DphpLvvIwg5aaC5p6c5rKh5pyJ5r+A5rS76K+354K55Ye75Lul5LiL6ZO+5o6lCiAgICAKICAgIGh0dHBzOi8vcmljaGFyZC5wdWIvCgoKQmVzdApSaWNoPart_690a405a-d366-48f4-a760-48433c5237d5--
.
TLS TCP 3次握手建立连接
TLS 建立加密链接，握手协议， Client Hello, ServerHello, CA , DH…
发送加密数据
参考
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