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1. For exchanges / social media account and any important account. Don't share this email to anyone else, please make sure that only you know this email. If someone knows this email address they will try to hack your account, even if you have 2fa on that exchange it will likely make your account lock, and if this your social media still probably fuck you up though.
2. For work/school. This means professional email, don't give it to anyone besides your college worker or friend from school.
3. For spam/promotional. You will use this email address for anything else, sign up for a newsletter, etc.
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In overall, I did agree with all the opinion you have mentioned.
However, based on my observations, i see (let say 7 out of 10 people) still using e-mail that provided by google, yahoo and kind like that.
My suggestion, if you do activities in crypto galaxy. It would be nice, if you using email platform that provider build their email platform based on blockchain technology.
Such as :
I have used tutanota since 1 year ago. When you create an email account at tutanota, then you will get a private key that has functions to restore your account. It function is exactly the same as wallet private key. So you have full control over the security of your account. Conversely, if you lose your private key, the email provider cannot help recovering your account. Coz they doesn't know your private key.
Conclusion, when you create an email account in above email provider that i mentioned, treat the private key you get same as like you treat your wallet private key.