The program is written in Xcode. After the program is run, send me an email to ask for help.

/*

Pure C mail program,

The default is 163 mailbox server, which can be modified,

By default, you need to manually enter the account number and Password,

Change the variable to a constant to automatically log in to the server using a fixed account.

Modify the receiving email account to send emails to the specified email address

Embed other c The c mail function can be implemented in the language code

*/

#include lt; windows.hgt;

#include lt; winsock.hgt;

#include lt;assert.hgt;

#include lt;iostreamgt;

#include lt;stringgt;

#include lt;stdio .hgt;

#include lt;ctimegt;

#pragma comment(lib, "WS2_32.lib")

using namespace std;

//base64 encoding

string Base64Encode(LPCTSTR lpszSrc);

//base64 decoding

string Base64Decode(LPCTSTR lpszSrc);

int main()

{

//1. First, you need to connect to the mail server. Here, use socket mail server port 25

WSADATA Wsa;

//Configure WINSOCK

WSAStartup(0x0101, amp; Wsa);

SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);

SOCKADDR_IN sin;

LPHOSTENT lphost = gethostbyname("smtp.163.com"); //This can also be modified using NetEase's mail server

if(lphost)

sin.sin_addr.s_addr = ((LPIN_ADDR)lphost-gt;h_addr)-gt;s_addr;

else

{

printf("s\n","Failed to obtain address");

return 1;

}

sin.sin_family = AF_INET;

//Pay attention to the listening port 25 of the mail server

sin.sin_port = htons(IPPORT_SMTP);

//Connect to the server

if( connect(s, (LPSOCKADDR)&sin, sizeof(sin))==SOCKET_ERROR)

{

printf("s\n","Connection Error");

return 1;

}

printf("s\n", "Connection successful");

//Receive the server for the first time Response

char buff[1024];

memset(buff, 0, sizeof(buff));

recv(s,

buff, sizeof(buff), 0);

printf("Service said: s\n", buff);

/////The above connection has been completed// ///

string szLine="\r\n"; //Equivalent to pressing Enter

//2. Now you are talking to the server

//Hello server

string szHelo = "HELO smtp.163.com" szLine;

printf("I said: s\n", szHelo.c_str() );

send(s, szHelo.c_str(), szHelo.length(), 0);

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

printf("Service said: s\n", buff);

//Request verification User password (encoding required)

string szAL = "auth login" szLine; //Send verification command

printf("I said: s\n", szAL.c_str() );

send(s, szAL.c_str(), szAL.length(), 0);

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

//printf("Service said: s\n", buff); //The server will reply that it can enter the account number

//Send account

string szUser;

coutlt;lt; Base64Decode((LPCTSTR)(buff 4));

cingt; gt; szUser;

szUser = Base64Encode(szUser.c_str()) szLine; // Base64 encode the input account

send(s, szUser.c_str() , szUser.length(), 0); //Send account

printf("I said: s\n", szUser.c_str());

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

// printf("Service said: s\n", buff ); //The server will reply that you can enter the password

//Send password

string szPsw;

coutlt;lt;Base64Decode((LPCTSTR)(buff 4));

cingt; gt; szPsw;

szPsw = Base64Encode(szPsw.c_str()) szLine; // Base64 encode the entered password

send(s, szPsw.c_str(), szPsw.length(), 0); //Send password

printf("I said: s\n", szPsw.c_str());

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

p>printf("Service said: s\n", buff);

//Then you can use the email address you logged in to send emails to other email addresses

string szFrom, szTo;

coutlt;lt;"from:";//your own email

cingt;gt;szFrom;

coutlt;lt;"to:" ; //Who to send to

cingt;gt;szTo;

//Sender's address

string From = "mail from: lt;" szFrom "gt;" szLine;

//Recipient address

string To = "rcpt to:lt;" szTo "gt;" szLine;

/ /Now determine who sent the email to where

send(s, From.c_str(), From.length(), 0); //from

printf(" I said: s\n", From.c_str());

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff) ), 0);

printf("Service said: s\n", buff);

getchar(); //Just used to pause, press any letter to continue

send(s, To.c_str(), To.length(), 0); //to

printf("I said: s\n", To.c_str( ));

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

printf("Service said: s\n", buff);

getchar();

//You should have read all the information. After inputting the data in the command, it means entering the email. Content

send(s, "data\r\n", 6, 0); //DATA command sent

printf("I said: s\n"," data");

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

printf("Service said: s\n", buff);

//The information below the email is treated as content

//Email header

string szFrom_in = "from:" szFrom szLine;

string szTo_in = "to:" szTo szLine;

//Sending date

string szDate_in= "Date: Sat, 20 Aug 2011 13:39:29 0800" szLine; //Here I will write the date directly for convenience

//Email title

string szSubject_in = "Subject: I am the email title" szLine;

//Email text

string szBody_in = "I am the legendary email body" szLine;

string szContent = szFrom_in szTo_in

szDate_in szSubject_in;

szContent = szLine; //Add a blank line

szContent = szBody_in;

//The above is the most basic format //

send(s, szContent.c_str(), szContent.length(), 0); //szContent

printf("I said: s\n", szContent.c_str() );

memset(buff, 0, sizeof(buff));

// recv(s, buff, sizeof(buff), 0);

// printf("Service said: s\n", buff);

getchar();

//end after sending instructions

send (s, ".\r\n", 3, 0); //The description is over

printf("I said: s\n", ".");

memset(buff, 0, sizeof(buff));

recv(s, buff, sizeof(buff), 0);

printf("Service said: s\ n", buff);

getchar();

//Exit the server connection

send(s, "quit\r\n", 6, 0); //Exit

printf("I said: s\n", "quit");

memset(buff, 0, sizeof(buff));

p>

recv(s, buff, sizeof(buff), 0);

printf("Service said: s sent email successfully\n", buff);

return 0;

}