这是mailcow自建邮局系列的第二篇教程，出于网络传输安全考虑，有必要对邮局启用TLS/SSL加密，这时候就需要用到SSL证书。
mailcow自动申请SSL证书
mailcow部署完毕后会自动使用ACME申请SSL证书，但前提是您使用的默认WEB端口80（Let’s Encrypt验证需要），如果非默认端口，则无法申请。也或者其它原因（如网络原因）可能导致申请失败。
由于磊大并未使用默认的80端口，因此就无法使用mailcow的自动SSL证书申请，我们也可以自行申请SSL证书后部署到mailcow，这样更加靠谱。
申请SSL证书
上一篇文章提到，如果您主机名设置为mail.domain.com，那么去申请SSL证书的时候也需要用这个域名（注意是二级域名，不是顶级域名），申请SSL证书这篇文章不做详细介绍。目前腾讯云、阿里云均提供免费的DV SSL证书，可以参考：
使用自己的SSL证书
磊大使用的是腾讯云免费SSL证书，申请完毕后下载Nginx的格式保存到本地。里面应该有4个文件，不过我们只会用到.crt和.key这两个后缀结尾的文件。
然后将.crt后缀的文件命名为cert.pem,将.key后缀的文件命名为key.pem并上传到mailcow目录下的data/assets/ssl目录进行替换。
注意：替换前可以将原来的文件备份，另外不要使用软连接。
然后修改mailcown.conf这个配置文件，将:
SKIP_LETS_ENCRYPT=n修改为
SKIP_LETS_ENCRYPT=y最后重启受影响的3个容器：
docker restart $(docker ps -qaf name=postfix-mailcow)
docker restart $(docker ps -qaf name=nginx-mailcow)
docker restart $(docker ps -qaf name=dovecot-mailcow)验证
输入下面的命令查看和验证SSL证书是否有效：
# 验证SMTP TLS端口
echo "Q" | openssl s_client -starttls smtp -crlf -connect mail.domain.com:587
#验证IMAP端口
echo "Q" | openssl s_client -starttls imap -showcerts -connect mail.domain.com:143
#验证HTTPS
echo "Q" | openssl s_client -connect mail.domain.com:443注意：请将mail.domain.com改成你自己的域名。
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