项目场景：
java mail集成james邮件服务器，发送邮件时需要判断邮件是否发送成功。我们会发现JavaMail给用户发送邮件，但是调用Transport类的sendMessage方法发送的邮件是没有返回值的，所以判断不了。但是我们可以用另一个解决方案，就是采用“系统退信”的方式来达到目的，我们会发现163、qq等邮件发送失败就会“系统退信”。
需求
什么情况下会系统退信
邮箱地址错误或访问不通；邮箱地址正确，但是用户不存在；
解决方案：
修改james配置，windows文件路径：james\apps\james\SAR-INF\config.xml，搜索关键字：maxRetries
原内容：
<mailet match="All" class="RemoteDelivery"><outgoing>file://var/mail/outgoing/</outgoing><!-- Delivery Schedule based upon RFC 2821, 4.5.4.1 --><!-- 5 day retry period, with 4 attempts in the firsthour, two more within the first 6 hours, and thenevery 6 hours for the rest of the period. --><delayTime> 5 minutes </delayTime><delayTime> 10 minutes </delayTime><delayTime> 45 minutes </delayTime><delayTime> 2 hours </delayTime><delayTime> 3 hours </delayTime><delayTime> 6 hours </delayTime><maxRetries> 25 </maxRetries><!-- The number of threads that should be trying to deliver outgoing messages --><deliveryThreads> 50 </deliveryThreads><!-- If false the message will not be sent to given server if any recipients fail --><sendpartial>false</sendpartial><!-- By default we send bounces to the "bounce" processor --><!-- By removing this configuration James will fallback to hardcoded bounce --><!-- notifications --><bounceProcessor>bounces</bounceProcessor>
</mailet>修改后的内容：
<mailet match="All" class="RemoteDelivery"><outgoing>file://var/mail/outgoing/</outgoing><!-- Delivery Schedule based upon RFC 2821, 4.5.4.1 --><!-- 5 day retry period, with 4 attempts in the firsthour, two more within the first 6 hours, and thenevery 6 hours for the rest of the period. --><delayTime> 1 minutes </delayTime><maxRetries> 1 </maxRetries><!-- The number of threads that should be trying to deliver outgoing messages --><deliveryThreads> 50 </deliveryThreads><!-- If false the message will not be sent to given server if any recipients fail --><sendpartial>true</sendpartial><!-- By default we send bounces to the "bounce" processor --><!-- By removing this configuration James will fallback to hardcoded bounce --><!-- notifications --><bounceProcessor>bounces</bounceProcessor>
</mailet>其实就是改了delayTime、maxRetries、sendpartial这三个标签
......<delayTime> 1 minutes </delayTime>
<maxRetries> 1 </maxRetries><sendpartial>true</sendpartial>......
解析：
这段内容就是邮件发送失败，重试的机制，这个outgoing文件夹里面就是需要重试的邮件
delayTime：重试的时间
maxRetries：最大重试次数
sendpartial：如果为true，任何收件人失败，会将消息发送到给定的服务器
所以原来默认是：
5天重试期，第一次尝试4次小时，前6小时内再增加两次，然后在剩余时间内，每6小时一次。
需要重试5天，时间太长了
我们改为了1分钟后只重试1次
我测试这应该是最短的间隔了，试了0.5minutes和1second好像没效果。
结果：
接收退信，就平时接收邮件一样就行了，在inboxes文件夹
邮箱地址错误或访问不通，测试的邮箱地址：test@test.com，系统退信的邮件内容Hi. This is the James mail server at XT-PC. I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. Below I include the list of recipients and the reason why I was unable to deliver your message.Failed recipient(s): test@test.comError message: There are no DNS entries for the hostname test.com. I cannot determine where to send this message.
邮箱地址正确，但是用户不存在，测试的邮箱地址：test1111@163.com，系统退信的邮件内容Hi. This is the James mail server at XT-PC. I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. Below I include the list of recipients and the reason why I was unable to deliver your message.Failed recipient(s): test1111@163.comError message: 550 User not found: test1111@163.com
总结：
缺点：不能实时反馈发送的结果
