SMTP 認證問題: Client does not have permission to Send As this sender

SMTP client 失敗原因, 很多套都是，以現在很多都開啟 SMTP 驗證 server來說...

smtpAuthLogin(dsocket *sd, const char *user, const char *pass)
{
      int retval = 0;
      dstrbuf *data;
      dstrbuf *rbuf = DSB_NEW;

      data = mimeB64EncodeString((u_char *)user, strlen(user), false);
      if (writeResponse(sd, "AUTH LOGIN %s\r\n", data->str) < 0) {
              smtpSetErr("Socket write error: smtp_auth_login");
              retval = ERROR;
              goto end;
      }

#ifdef DEBUG_SMTP
      printf("--> AUTH LOGIN\n");
      fflush(stdout);
#endif

      retval = readResponse(sd, rbuf);
      if (retval != 334) {
              if (retval != ERROR) {
                      smtpSetErr(rbuf->str);
              }
              retval = ERROR;
              goto end;
      }

#ifdef DEBUG_SMTP
      printf("<-- %s\n", rbuf->str);
      fflush(stdout);
#endif

      /* Encode the password */
      dsbDestroy(data);

將

AUTH LOGIN %s

拆成兩個動作，以兩次的command 來回，就可以解決這個問題了

• Client does not have permission to Send As this sender

Reference:

• SmtpClient 身份验证失败(authentication failed) 的原因分析
• email-3.1.2 ( smtpcommands.c )