如何使用java发送电子邮件

Question

我正在尝试使用java邮件发送电子邮件。但是当我运行下面的代码时，我会得到大量的错误。你能向我解释一下为什么代码不起作用吗。所以我想做的是用java发送一封电子邮件。如果还有其他办法，你能告诉我吗。我猜smpt服务器出了问题。我是新来的堆栈溢出，所以请原谅我没有写正确的问题。

编辑：我现在明白哪里出了问题——我的本地主机上没有运行SMPT服务器。有人能解释一下如何免费创建SMPT服务器吗

这些是我遇到的错误

/home/theprogrmmer/.jdks/openjdk-15.0.1/bin/java -javaagent:/home/theprogrmmer/.local/share/JetBrains/Toolbox/apps/IDEA-U/ch-0/202.8194.7/lib/idea_rt.jar=44243:/home/theprogrmmer/.local/share/JetBrains/Toolbox/apps/IDEA-U/ch-0/202.8194.7/bin -Dfile.encoding=UTF-8 -classpath /home/theprogrmmer/IdeaProjects/practice 1/out/production/practice 1:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.ejb.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.jms.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.annotation.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.persistence.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.resource.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.transaction.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.servlet.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.servlet.jsp.jar:/home/theprogrmmer/IdeaProjects/practice 1/lib/javax.servlet.jsp.jstl.jar:/home/theprogrmmer/IdeaProjects/practice 1/src/com/company/mail.jar:/home/theprogrmmer/IdeaProjects/practice 1/src/com/company/jaf-1.0.2/activation.jar com.company.SendEmail
javax.mail.MessagingException: Could not connect to SMTP host: localhost, port: 25;
nested exception is:
java.net.ConnectException: Connection refused
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1961)
at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:654)
at javax.mail.Service.connect(Service.java:295)
at javax.mail.Service.connect(Service.java:176)
at javax.mail.Service.connect(Service.java:125)
at javax.mail.Transport.send0(Transport.java:194)
at javax.mail.Transport.send(Transport.java:124)
at com.company.SendEmail.main(SendEmail.java:48)
Caused by: java.net.ConnectException: Connection refused
at java.base/sun.nio.ch.Net.connect0(Native Method)
at java.base/sun.nio.ch.Net.connect(Net.java:574)
at java.base/sun.nio.ch.Net.connect(Net.java:563)
at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:588)
at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:333)
at java.base/java.net.Socket.connect(Socket.java:648)
at java.base/java.net.Socket.connect(Socket.java:597)
at com.sun.mail.util.SocketFetcher.createSocket(SocketFetcher.java:321)
at com.sun.mail.util.SocketFetcher.getSocket(SocketFetcher.java:237)
at com.sun.mail.smtp.SMTPTransport.openServer(SMTPTransport.java:1927)
... 7 more

这是我的java代码

package com.company;
// File Name SendEmail.java
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import javax.activation.*;
public class SendEmail {
public static void main(String [] args) {
// Recipient's email ID needs to be mentioned.
String to = "[e-mail]";
// Sender's email ID needs to be mentioned
String from = "[e-mail]";
// Assuming you are sending email from localhost
String host = "localhost";
// Get system properties
Properties properties = System.getProperties();
// Setup mail server
properties.setProperty("mail.smtp.host", host);
// Get the default Session object.
Session session = Session.getDefaultInstance(properties);
try {
// Create a default MimeMessage object.
MimeMessage message = new MimeMessage(session);
// Set From: header field of the header.
message.setFrom(new InternetAddress(from));
// Set To: header field of the header.
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
// Set Subject: header field
message.setSubject("This is the Subject Line!");
// Now set the actual message
message.setText("This is actual message");
// Send message
Transport.send(message);
System.out.println("Sent message successfully....");
} catch (MessagingException mex) {
mex.printStackTrace();
}
}
}

Answer 1

设置仅本地SMTP电子邮件服务器(Linux、Unix、Mac(

1-将localhost.com指向您的机器

大多数程序都不会接受仅使用@localhost作为域的电子邮件。因此，编辑/etc/hosts文件，使域localhost.com指向您的机器，包括以下内容到文件：

127.0.0.1 localhost.com

2-安装Postfix

Fedora/COS/RHEL:sudo yum-install-postfix

Ubuntu：sudo apt-get-install postfix

MacOSX:Postfix默认情况下已经安装。

3-将Postfix配置为仅本地

During postfix install process, the configure text dialog will display five options:
General type of mail configuration: 
No configuration
Internet Site
Internet with smarthost
Satellite system
Local only
Select "Local Only".
For the domain name, use the default suggested and finish the install.

4-配置Catch-all地址

启用此功能后，您可以使用任何以"结尾的电子邮件地址@localhost"；或"@localhost.com"；。

示例：在这里，我的唯一帐户是[e-mail].但在测试系统时，我可以使用任何地址[e-mail]，[e-mail]，等等，因为所有内容都将重定向到[e-mail]

If not exists, create file /etc/postfix/virtual: sudo nano /etc/postfix/virtual
Add the following 2 lines content, replacing <your-user> with your Unix user account:

@[e-mail]

Save and close the file.
Configure postifx to read this file:
Open /etc/postfix/main.cf: sudo nano /etc/postfix/main.cf
And check if this line is enabled, or add it if not exists: virtual_alias_maps = hash:/etc/postfix/virtual
Activate it: sudo postmap /etc/postfix/virtual
Reload postfix: sudo systemctl restart postfix
If you're under non systemd distro, like Ubuntu 14.04, service restart command probably is: sudo service postfix reload

5-安装Thunderbird

Ubuntu:sudo apt-get安装thunderbird

6-配置Thunderbird

Skip the welcome screen (click in the button to use existing accounts);
Click in the Settings button at top right (similar to Chrome settings) then click on Preferences > Account Settings
Under Account Actions choose "Add Other Account"
Select "Unix Mailspool (Movemail)"
Your account will be <your-user>@localhost (of course, replace <your-user> with your user account). Don't use <your-user>@(none), use <your-user>@localhost
Ingoing and Outgoing server will be: localhost
Restart (close and reopen) Thunderbird.

7-启动邮件后台文件

This step have two purposes: test your install and stop the Unable to locate mail spool file. message.
Using Thunderbird, send new email to <your-user>@localhost, replacing <your-user> with your user account
Click on "Get Mail"
Test catch-all: send new email to averagejoe@localhost
Click on "Get Mail" and you'll see the message at Inbox.