wordpress跑在vultr上，邮件一直没发成功。从vps本身发送出的测试邮件不说，因为其他邮箱就算没收到也懒得排查到底是被对方服务商ban了还是没发成功（因为个人邮件服务器折腾很烦，要打通各个关节）。然而使用第三方smtp插件（比如WP-Mail-SMTP）借道qq邮箱、阿里邮箱、163邮箱居然都没能让对方成功收到邮件，总是报错，还以为是用的宝塔面板在vultr上对smtp函数支持有问题。折腾了一天，意外看到vultr默认封锁25等邮件端口的文章。于是提交ticket申请开放smtp，解封后即可正常使用第三方smtp发送邮件。
VULTR FAQ https://www.vultr.com/faq/：
| Port X seems to be blocked on my VPS, are you blocking it? We block several ports that are commonly abused for DDOS attacks. This includes TCP and UDP ports 17, 19, 1900. These blocks are permanent, and cannot be removed. Depending on your account, outbound 53413 UDP and SMTP (port 25) may also be blocked. This block may be removed by opening a support ticket. Also note that many operating systems are configured with firewalls which block traffic. You would need to open any ports you need within your VPS's firewall. |
| Do you allow outbound SMTP? In some instances, outbound traffic to the SMTP port may be blocked for new accounts. If you encounter this restriction, contact our support team from the customer portal. |
处理经过：
【时间17:00】提交ticket：please unblock port 25，My wp blog needs to use smtp，thank you。
【时间17:25】收到处理回复（取消了对stmp的封锁，去vultr后台重启生效，注意：在服务器中重启无效）：
|
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Hello, I have removed the default SMTP block on your account. Please restart any active instances via https://my.vultr.com for the change to take effect (restarting via the server itself _will_not_ work). |
客服处理后，smtp可正常使用了。
BackWPup邮件测试从QQ邮箱发送成功【17年9月9日18:31】
从阿里邮箱smtp发送成功【不支持ssl，只能使用25】
