r = rcpthosts(addr.s,str_len(addr.s));  if (r == -1) die_control();  return r;}int seenmail = 0;int flagbarf; /* defined if seenmail */stralloc mailfrom = {0};stralloc rcptto = {0};void smtp_helo(arg) char *arg;{  smtp_greet("250 "); out("\r\n");  seenmail = 0; dohelo(arg);}void smtp_ehlo(arg) char *arg;{  smtp_greet("250-"); out("\r\n250-PIPELINING\r\n250 8BITMIME\r\n");  seenmail = 0; dohelo(arg);}

//重新初始化，調用helo或ehlo命令都會完成相同的功能void smtp_rset(){  seenmail = 0;  out("250 flushed\r\n");}

//mail命令解釋程序，重要變量：[mailfrom/全局]
//該函數完成檢查mailfrom是否在badmailfrom中定義，設置標志指明mail命令已經執行void smtp_mail(arg) char *arg;{  if (!addrparse(arg)) { err_syntax(); return; }

  //檢查是否badmailfrom，如果是設置相應標志，這個標志在rcpt命令的處理程序中才起作用  flagbarf = bmfcheck();  seenmail = 1;		//指示已經執行過mail命令。  if (!stralloc_copys(&rcptto,"")) die_nomem();		//分配rcptto緩沖區  if (!stralloc_copys(&mailfrom,addr.s)) die_nomem();	//復制mail命令中指定的地址到mailfrom  if (!stralloc_0(&mailfrom)) die_nomem();  out("250 ok\r\n");}

//rcpt命令解釋程序，重要變量：[rcptto/全局]void smtp_rcpt(arg) char *arg; {  if (!seenmail) { err_wantmail(); return; }	//買了命令是否已經執行？  if (!addrparse(arg)) { err_syntax(); return; }	//分離郵件地址參數存入全局緩存addr  
  //如果mail命令中的地址在control/badmailfrom中有定義，返回
  if (flagbarf) { err_bmf(); return; }
  //至此addr緩存中包含了rcpt命令指定的email地址
  //如果rcpt命令，則有addr="email@eg.org"。這個變量是在addrparse函數中賦值的
  //如果RELAYCLIENT環境變量設置將不進行rcpthosts，morercpthosts.cdb的比較
  //足以，大國smtp認證補丁，如果通過認證后會設置relayclient=""  if (relayclient) {    --addr.len;    if (!stralloc_cats(&addr,relayclient)) die_nomem();    if (!stralloc_0(&addr)) die_nomem();  }  else		//如果沒有指定RELAYCLIENT變量，則有control/rcpthosts決定是否進行轉發    if (!addrallowed()) { err_nogateway(); return; }

	//生成頭連接到全局緩存rcptto：
	//例如地址"rcpt test@eg.org"命令將產生rcptto="Temail@eg.org"
	//多次執行rcpt命令效果會是rcptto=“Ttest@eg.orgTtwo@eg.org”  if (!stralloc_cats(&rcptto,"T")) die_nomem();  if (!stralloc_cats(&rcptto,addr.s)) die_nomem();  if (!stralloc_0(&rcptto)) die_nomem();  out("250 ok\r\n");}
//saferead,從網絡讀len個字節到buf緩沖區
//返回實際讀到的字節數.
//超時值為control/timeoutsmtpd文件中指定的值.見setup()函數，(默認值1200秒)int saferead(fd,buf,len) int fd; char *buf; int len;{  int r;  flush();  r = timeoutread(timeout,fd,buf,len);  if (r == -1) if (errno == error_timeout) die_alarm();  if (r <= 0) die_read();  return r;}char ssinbuf[1024];substdio ssin = SUBSTDIO_FDBUF(saferead,0,ssinbuf,sizeof ssinbuf);struct qmail qqt;unsigned int bytestooverflow = 0;void put(ch)char *ch;{  if (bytestooverflow)    if (!--bytestooverflow)      qmail_fail(&qqt);  qmail_put(&qqt,ch,1);}void blast(hops)int *hops;{  char ch;  int state;  int flaginheader;  int pos; /* number of bytes since most recent \n, if fih */  int flagmaybex; /* 1 if this line might match RECEIVED, if fih */  int flagmaybey; /* 1 if this line might match \r\n, if fih */  int flagmaybez; /* 1 if this line might match DELIVERED, if fih */   state = 1;  *hops = 0;  flaginheader = 1;  pos = 0; flagmaybex = flagmaybey = flagmaybez = 1;  for (;;) {

	//從標準輸入(也就是網絡)讀郵件內容直到獨到僅有一個點的行.    substdio_get(&ssin,&ch,1);    if (flaginheader) {      if (pos < 9) {        if (ch != "delivered"[pos]) if (ch != "DELIVERED"[pos]) flagmaybez = 0;        if (flagmaybez) if (pos == 8) ++*hops;        if (pos < 8)          if (ch != "received"[pos]) if (ch != "RECEIVED"[pos]) flagmaybex = 0;        if (flagmaybex) if (pos == 7) ++*hops;        if (pos < 2) if (ch != "\r\n"[pos]) flagmaybey = 0;        if (flagmaybey) if (pos == 1) flaginheader = 0;      }      ++pos;      if (ch == '\n') { pos = 0; flagmaybex = flagmaybey = flagmaybez = 1; }    }    switch(state) {      case 0:        if (ch == '\n') straynewline();        if (ch == '\r') { state = 4; continue; }        break;      case 1: /* \r\n */        if (ch == '\n') straynewline();        if (ch == '.') { state = 2; continue; }        if (ch == '\r') { state = 4; continue; }        state = 0;        break;      case 2: /* \r\n + . */        if (ch == '\n') straynewline();        if (ch == '\r') { state = 3; continue; }        state = 0;        break;      case 3: /* \r\n + .\r */        if (ch == '\n') return;        put(".");        put("\r");        if (ch == '\r') { state = 4; continue; }        state = 0;        break;      case 4: /* + \r */        if (ch == '\n') { state = 1; break; }        if (ch != '\r') { put("\r"); state = 0; }    }    put(&ch);  }}char accept_buf[FMT_ULONG];void acceptmessage(qp) unsigned long qp;{  datetime_sec when;  when = now();  out("250 ok ");  accept_buf[fmt_ulong(accept_buf,(unsigned long) when)] = 0;  out(accept_buf);  out(" qp ");  accept_buf[fmt_ulong(accept_buf,qp)] = 0;  out(accept_buf);  out("\r\n");}
//data命令解釋程序
//完成向qmail-queue投遞郵件void smtp_data() {  int hops;  unsigned long qp;  char *qqx;   if (!seenmail) { err_wantmail(); return; }	//如果沒有執行過mail命令，出錯返回  if (!rcptto.len) { err_wantrcpt(); return; }	//如果沒有執行rcpt命令，出錯返回  seenmail = 0;		//將mail命令標志失效

  //databytes郵件最大長度，如果沒有指定那么值是0，代表無限  if (databytes) bytestooverflow = databytes + 1;  if (qmail_open(&qqt) == -1) { err_qqt(); return; }	//建立子進程執行qmail-queue  qp = qmail_qp(&qqt);		//qp為qmail-queue process縮寫，it's a process id。  out("354 go ahead\r\n"); 
  //向新建立的進程傳送郵件頭  received(&qqt,"SMTP",local,remoteip,remotehost,remoteinfo,fakehelo);  blast(&hops);  hops = (hops >= MAXHOPS);  if (hops) qmail_fail(&qqt);

  //向qmail-queue傳送郵件頭信息,如果hong@hg.org向lyx@hg.org發送郵件，那么向qmail-queue
  //傳送的字符串將是 Fhong@hg.orgTlyx@hg.org  qmail_from(&qqt,mailfrom.s);  qmail_put(&qqt,rcptto.s,rcptto.len);   qqx = qmail_close(&qqt);  if (!*qqx) { acceptmessage(qp); return; }		//如果接受成功  if (hops) { out("554 too many hops, this message is looping (#5.4.6)\r\n"); return; }  if (databytes) if (!bytestooverflow) { out("552 sorry, that message size exceeds my databytes limit (#5.3.4)\r\n"); return; }  if (*qqx == 'D') out("554 "); else out("451 ");  out(qqx + 1);  out("\r\n");}

//smtp命令處理函數表struct commands smtpcommands[] = {  { "rcpt", smtp_rcpt, 0 }, { "mail", smtp_mail, 0 }, { "data", smtp_data, flush }		//建立子進程執行qmail-queue，并向其傳送郵件., { "quit", smtp_quit, flush }, { "helo", smtp_helo, flush }, { "ehlo", smtp_ehlo, flush }, { "rset", smtp_rset, 0 }, { "help", smtp_help, flush }, { "noop", err_noop, flush }		//實際上未實現的命令, { "vrfy", err_vrfy, flush }		//實際上未實現的命令, { 0, err_unimpl, flush }			//命令錯誤} ;

/*
　　qmail-smtpd 是由tcp-env程序啟動
　　tcp-env將來自網絡的連接重定向到qmail-smtpd的標準輸入及標準輸出.
	這些程式建立一些環境變量(如TCPREMOTEHOST,TCPREMOTEIP)將由setup()函數使用
*/
void main(){  sig_pipeignore();		//忽略信號  if (chdir(auto_qmail) == -1) die_control();	//改變當前目錄到/var/qmail  setup();		//讀控制文件及相應的環境變量  if (ipme_init() != 1) die_ipme();		//取本地接口的ip地址  smtp_greet("220 ");		//顯示歡迎信息  out(" ESMTP\r\n");

  //從標準讀入(網絡連接)讀入smtp命令  if (commands(&ssin,&smtpcommands) == 0) die_read();  die_nomem();}