使用SMTP协议发送邮件,可以不通过SMTP服务器,直接将邮件发送到邮件服务器。很多服务器端程序可能需要向很多用户发送邮件,直接通过SMTP发送可能是最有效的。关于SMTP协议定义在RFC821,可以在此看中文版。第一步:通过目标email查找邮件服务器。例如:asklxf@sohu.com,其邮件服务器地址为:sohumx.sohu.com import java.net. * ; import java.io. * ; import java.util. * ; import javax.naming. * ; import javax.naming.directory. * ; public class Smtp ... { public static void main(String[] args) throws Exception ...{ // DNS服务器,看看本机的DNS配置 String dns = "dns://192.168.1.1"; // 邮箱后缀: String domain = "sohu.com"; Hashtable env = new Hashtable(); env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory"); env.put("java.naming.provider.url", dns); DirContext ctx = new InitialDirContext(env); Attributes attr = ctx.getAttributes(domain, new String[]...{"MX" }); NamingEnumeration servers = attr.getAll(); // 列出所有邮件服务器: while(servers.hasMore()) ...{ System.out.println(servers.next()); } } } 第二步:直接连接邮件服务器的25端口,用SMTP协议发送邮件。这里使用sohu信箱,邮件服务器为sohumx.sohu.com,收信人必须在此服务器上: import java.net. * ; import java.io. * ; import java.util. * ; import javax.naming. * ; import javax.naming.directory. * ; public class Smtp ... { private static String END_FLAG = " "; public static void main(String[] args) throws Exception ...{ String mx = "sohumx.sohu.com"; InetAddress addr = InetAddress.getByName(mx); Socket socket = new Socket(addr, 25); InputStream in = socket.getInputStream(); OutputStream out = socket.getOutputStream(); // 连接成功后服务器会响应: response(in); // 首先发送HELO命令: send("HELO www.javasprite.com" + END_FLAG, out); response(in); // 然后发送发件人地址: send("MAIL FROM: someone@somewhere.com" + END_FLAG, out); response(in); // 设置收件人地址: send("RCPT TO: asklxf@sohu.com" + END_FLAG, out); response(in); // 开始发送邮件正文: send("DATA" + END_FLAG, out); response(in); send("From: someone@somewhere.com" + END_FLAG, out); send("To: asklxf@sohu.com" + END_FLAG, out); send("Subject: Test without smtp server" + END_FLAG, out); send("Content-Type: text/plain;" + END_FLAG, out); send(END_FLAG + END_FLAG, out); // 发送邮件正文,如果用中文,需要BASE64编码: send("text message body!" + END_FLAG, out); // 每行以 结束,不可过长,可拆成多行。 // 以" . "作为结束标志: send(END_FLAG + "." + END_FLAG, out); response(in); // 结束并确认发送: send("QUIT" + END_FLAG, out); response(in); in.close(); out.close(); socket.close(); } public static void response(InputStream in) throws Exception ...{ byte[] buffer = new byte[1024]; int n = in.read(buffer); String s = new String(buffer, 0, n); // 服务器会返回:### Text // 具体含义见RFC821 System.out.println(s); } public static void send(String s, OutputStream out) throws Exception ...{ byte[] buffer = s.getBytes(); out.write(buffer); // 不要忘了flush(),否则可能在缓冲区: out.flush(); } } Ok,打开outlook收信,会发现有一封来自someone@somewhere.com的信件。第三步:处理服务器返回码,各种异常,包装成Java组件以便重用: public interface SendMail ... { void send(String from, String to, String subject, String text) } public class SendMailImpl extends Thread implements SendMail ... { // TODO: 自己写...... }