There is a balance to be had here. In a high volume, sensitive environment you'd run your own mail server. But that is a challenge in-and-of itself. I don't recommend it for a home setup because there are numerous things to worry about like MX forwarding and what happens if your server goes down -- where does the e-mail go? Granted, using Gmail means if your server is compromised the bad-actor would have your gmail password which is why I recommend enabling 2FA/MFA on Gmail and then using an app password. Check http://reddit.com/r/selfhosted if you want to self-host mail.

It's better than running your own smtp servers. But the article proposes using your own gmail account, to which the server has an app password. So a server compromise leads to your own email being compromised. It should be a separate gmail account.

So I use a separate gmail account for my server but forgot to mention in guide. I will add it.

Although I wonder if its necessary if you use an app password. What is the worst a bad-actor can do with the app password?