Send emails using SMTP

I,
Assuming that the sender jmst66 (jmst66@163.com) is sent to the neuwjyou@sina.com mailbox, the commands returned by the following hosts indicate the commands returned when the command succeeds. The sending process is as follows:

1. Connect to the host smtp.163.com
Host return: 220 163.com anti-spam GT for coremail System (163com [20050206])

2. First session
Send command: EHLO mailto: jmst66@163.com % 20R % 20n (Note: After the command is sent, there is a line feed identifier "/R/N ")
Returned data:
250-mail
250-pipelining
250-auth login Plain
250-auth = login Plain
250 8 bitmime

3. User Logon
Send command: auth login/R/n
Returned data: 334 dxnlcm5hbwu6 (Note: This is the base64 encoding of username)
Sending account: am1zddy2 (base64 encoding of jmst66)

Returned data: 334 ugfzc3dvcmq6 (Note: This is the base64 encoding of password)
Sending password: xxxxxxx (base64 encoding of the password of jmst66)

Returned data: 235 authentication successful (logon successful)

4: email sending instructions
Send command: mail from: <mailto: jmst66@163.com> % 20R % 20n
Returned data: 250 mail OK

5. Description of the target email address
Send command: rcpt to: <mailto: neuwjyou@sina.com> % 20R % 20n
Returned data: 250 mail OK

6. send an email request
Send command: Data/R/n
Return command: 354 end data with <CR> <LF>. <CR> <LF>

7. Send the mail header and body
Send data: the complete data is directly ended with "<CR> <LF>. <CR> <LF>"
Returned data: 250 mail OK queued as smtp1, wkjrc7d7f6mfoodga_i7ma =. 52140s2 1189584903

8. End sending data
Send command: Quit/R/n
Receive data: 221 bye

9. Disconnect

II,
The specific program implementation is briefly described as follows:
1. Connect to the host smtp.163.com

Sockaddr_in serveraddr;
Socket sock;
Hostent * Host;
Host = gethostbyname (serverhostname. c_str ());
If (host = NULL ){
Return-1;
}

Sock = socket (af_inet, sock_stream, 0 );
Serveraddr. sin_addr = * (struct in_addr *) Host-> h_addr;
Serveraddr. sin_family = af_inet;
Serveraddr. sin_port = htons (SERVERPORT );

If (connect (sock, (const sockaddr *) & serveraddr, sizeof (sockaddr) = socket_error)
{
Closesocket (sock );
Return-1;
}

// Add a value to determine whether the data returned by the host indicates success
Deal_return_code (getresponsecode (sock, 220, STR ));

2. First session
Char buffer [buffer_size];
Sprintf (buffer, "ehlo % S/R/N", from); // from is Char data. Storage sending Address
Send (sock, buffer, strlen (buffer), 0 );

3. User Logon
Sprintf (buffer, "auth login/R/N ");
Send (sock, buffer, strlen (buffer), 0 );

// User Name
// User name is coded by base64.
Encodingbase64 (username. c_str (), buffer); // encode the user account with base64
Strcat (buffer, "/R/N ");
Send (sock, buffer, strlen (buffer), 0 );

// Password coded by base64
Encodingbase64 (Pass. c_str (), buffer); // encode the password with base64
Strcat (buffer, "/R/N ");
Send (sock, buffer, strlen (buffer), 0 );

4: email sending instructions
Sprintf (buffer, "mail from: <% S>/R/N", from. c_str ());
Send (sock, buffer, strlen (buffer), 0 );

5. Description of the target email address
Sprintf (buffer, "rcpt to: <% S>/R/N", to. c_str ());
Send (sock, buffer, strlen (buffer), 0 );
Deal_return_code (getresponsecode (sock, 250, STR ));

6. send an email request
Sprintf (buffer, "Data/R/N ");
Send (sock, buffer, strlen (buffer), 0 );
Deal_return_code (getresponsecode (sock, 354, STR ));

7. Send the mail header and body. The subject part of the sent mail should be formatted before being sent. The format program is not described here.
// Data head
Send (sock, mailhead, strlen (mailhead), 0 );

// Data body
Send (sock, mailbody, strlen (mailbody), 0 );

8. End sending data
Strcpy (buffer, "Quit/R/N ");
Send (sock, buffer, strlen (buffer), 0 );
Deal_return_code (getresponsecode (sock, 221, STR ));

9. Disconnect
Closesocket (sock );

}

Mail header, composed
Date:
From:
To:
Subject:
Message-ID:
X-mailer:
Mime-version:

The following is the encoded data of an email:

Date: Wed, 12 Sep 2007 16:13:56 + 0800
From: <jmst66@163.com>
To: <zzzheng@hit.edu.cn>
Subject: =? Gb2312? B? Sk1tvcc52npat6kx7c7e1ck78b2xtfey6q ==? =
Message-ID: <1189584836@163.com>
X-mailer: =? Gb2312? B? 19s8urxetwfpbgvy? =
Mime-type: 1.0
Content-Type: multipart/alternative;
???????? Boundary = "=== majorsplittag ==="
This is a multi-part message in MIME format.

-- === Majorsplittag ===
Content-Type: text/plain;
???????? Charset = "gb2312"
Content-transfer-encoding: base64

-- === Majorsplittag ===
Content-Type: text/html;
???????? Charset = "gb2312"
Content-transfer-encoding: base64

Pgh0bww + Signature
Bytes
Zd4nc1_kpgjvzhk + dqo8zm9udcbzaxplpsirmsi + dqo8ccbhbglnbj0ibgvmdci + 1/C + tlxe1/fv36os
Bytes/s
Qsrvvk/e + ttaobzktvnuobe3orhtwtvoxlxez + c52ndfz6kjrmbk1tcw/mcou/g9scfpv/ajrm7e1ckx
U9l908o1xltoyv26zbg70v3tw7xev6/o78p7s8ajrlvy1d + 78deowpvj6sfrtctwpmrpoaph68t6vavl
+ Beise3oxnxctctm4ss/o6ziq7k/1/fv36ost6kx7bxeicde6qosvu2jqmbao6mjrznkilyw0 + u45bz +
Z + c52lxeu/g9sdakyum78txf16ja + 9 akyumjrmmow + i687eiy83wwtx1pkpnu1q2nkaxnjmuq29tpc91
Prvy1d + 9q8bkulttobz + tkvv5tbbiko6idaynkotodm5nzkyndihoya8l3a + dqo8ccbhbglnbj0ibgvm
DCI + 1/fv37xeynnt/tkyysfo0sphxtq/r7xeynnt/qost8ezo7jq0lve + rbuztldx7mk1/e1xmxkus + J
Rnkyz6pn + 8t6us3e + rxezazkwsphxnzsu8jnvmjn + bxy1qez1s7sw8ejosa8l3a + dqo8ccbhbglnbj0i
Bgvmdci + 16pe + qo6ilmk1/fls8d7o6zn8srcyofs4qohidxiciavpg0kicc0y9bcidwvcd4ncjxwifs
Awdupsjszwz0ij6 + tmdxidwvcd4ncjxwiggfsawdupsjszwz0ij5ktvnusec8rbk/idwvcd4nc1_vzm9u
Bytes
Ls0tls0tls0gpgjyic8 + dqogiepvdxjuywwgb2ygtwf0zxjpywxzicbty2llbmnliczhbxa7ifrly2hu
Bytes
Bytes
Bytes
Ci5hyy5jbii + sk1tvebpbxiuywmuy248l2e + lca8ysbocmvmpsjtywlsdg86sk1tvdy2qde2my5jb20i
Pkpnu1q2nkaxnjmuy29tpc9hpia8l3a + dqo8ccbhbglnbj0ibgvmdci + v2viia8ysbocmvmpsjodhrw
Oi8vd3d3lkpnu1qut1jhij5xv1cusk1tvc5pukc8l2e + idxiciavpg0kicatls0tls0tls0tls0tls0tls0t
Bytes
-- === Majorsplittag ===

Base64 encoding is actually to convert three 8-bit bytes into four 6-bit bytes ,(? 3*8? =? 4*6? =? 24 ?)? What are the four six bytes? In fact, it is still 8 bits, but the upper two bits are set to 0 .? When a byte is valid for only 6 characters, its value is 0? To? Is the power 6 of 2 reduced by 1? That is, 63, that is, the value space of each encoded base64 to be converted is (0 ~ 63 )?.?
????
???? In fact, 0 ~ There are many invisible characters in the ASCII code between 63, so we should make another ing. The ing table is?
????
???? 'A '?~? 'Z '??? ASCII (0 ?~? 25 )?
????
???? 'A '?~? 'Z '??? ASCII (26 ?~? 51 )?
????
???? '0 '?~? '9 '??? ASCII (52 ?~? 61 )?
????
???? '+ '??? ASCII (62 )?
????
???? '/'??? ASCII (63 )?
????
???? In this way, three 8-bit bytes can be converted to four visible characters .?
????
???? The specific byte splitting method is as follows? :-))?
????
???? Aaaaaabb? Ccccdddd? Eeffffff ??? // Abcdef is actually 1 or 0. Use abcdef instead to make it clear.
????
???? ~~~~~~~~?~~~~~~~~?~~~~~~~~?
????
???? Bytes? 1? Bytes? 2? Bytes? 3?
????
???? |?
???? //?
????
???? 00 aaaaaa? 00 bbcccc? 00 ddddee? 00 ffffff?
????
???? Note: The above three bytes are original. The following four bytes are base64 encoded, and the first two are both 0 .?
????
???? In this case, the number of bytes in the original text should be a multiple of 3. When this condition cannot be met, the full zero byte is used?
????
???? Complete. The base64 encoding is replaced by the = sign during conversion. That is why some base64 encoding ends with one or two equal signs?
????
???? Because F (origin) represents the number of bytes in the original text, F (remain) represents?
????
???? Table remainder, then?
????
???? F (remain )? =? F (origin )? MoD? 3? Yes .?
????
???? So the possible values of F (remain) are 0, 1, 2 .?
????
???? If you set? N? =? [F (origin )? -? F (remain)]? /? 3?
????
???? When F (remain )? =? 0? Is converted to 4 * n Bytes of base64 encoding .?
????
???? When F (remain )? =? 1? Because a Source byte can be split into two base64 encoded bytes?
????
???? So that base64 encoding is a multiple of 4, so we should add two equal signs .?
????
???? When F (remain )? =? 2? Because two original bytes can be split into three base64 encoded bytes, the same is true ,?
????
???? An equal sign should be added.