Glad to have you here in the QuickBooks Community, @cong-gao.
It's good to know that you've received the validation code to your personal email (Gmail) account and successfully register to QuickBooks Online.
Please know that you can use any different email servers in QuickBooks. If you can't find the emails coming from us, you'll want to make sure to check your spam and junk folders first.
Validation code emails come from do_not_reply@intuit.com during sign-in and usually take 1 to 2 minutes before you receive it. If the email doesn't appear after 10 minutes, contact your email provider to evaluate security settings for your email profile.
I'm adding this article for more details: Receive important email messages from Intuit.
As always, feel free to visit our QuickBooks Community help website if you need tips and related articles in the future.
Keep in touch if you need any more assistance with this, or there's something else I can do for you. I've got your back. Have a good day.
