"Sign in with Twitter" provides you with a confirmed email address. I'm pretty sure that when a user has not confirmed their email address the Twitter OAuth flow won't provide the email. (I ran into a bug related to this, hence I looked into it).
The same is probably true for Facebook and many other OAuth services. Just make sure to double check they don't provide you with unconfirmed email addresses (i.e. create a test account to see what happens).
Another more novel, but not fool-proof way to verify an email address is to have the user send you an email. I one saw an "email sign up forms" that was just a mailto: link. When the user sends an email to that address he/she got subscribed to the newsletter. However, it's not fool-proof since it can be faked.
In addition to what @ronald93 says:
"Sign in with Twitter" provides you with a confirmed email address. I'm pretty sure that when a user has not confirmed their email address the Twitter OAuth flow won't provide the email. (I ran into a bug related to this, hence I looked into it).
The same is probably true for Facebook and many other OAuth services. Just make sure to double check they don't provide you with unconfirmed email addresses (i.e. create a test account to see what happens).
Another more novel, but not fool-proof way to verify an email address is to have the user send you an email. I one saw an "email sign up forms" that was just a
mailto:link. When the user sends an email to that address he/she got subscribed to the newsletter. However, it's not fool-proof since it can be faked.