CNAME 验证
dns解析记录截图
https://support.google.com/a/answer/172171?hl=en&ref_topic=9202
MX记录
tool https://admin.google.com/u/0/ac/signup/setup/v2/gettingstarted
DKIM 记录
全局设置
管理员给全局开两步验证（非强制）
个人开两步验证，使用应用密码
限制
DMARC/ SPF/ DKIM
https://support.google.com/a/topic/9061731?hl=en&ref_topic=9202&sjid=2170326043448675934-AP
POP SMTP
Go to your client, like Microsoft Outlook, and check these settings.
Incoming Mail (POP) Server
pop.gmail.com
Requires SSL: Yes
Port: 995
Outgoing Mail (SMTP) Server
smtp.gmail.com
Requires SSL: Yes
Requires TLS: Yes (if available)
Requires Authentication: Yes
Port for TLS/STARTTLS: 587
