Design a database table first
EmailTokens for example, that can be something like this.
UserID(int), Token(String/Varchar), Created_At(Date).
Also, create a player value for whether or not the email is verified: EmailVerified(Boolean).
When a user inserts their email address, generate a random token and insert it into the EmailTokens table.
So that, if userID
32 adds email
myemail@provider.gg the table gets a new entry that would look like this.
[
32,
myemail@provider.gg,
1499352423] <-- unix timestamp.
Make all three of them combined to be the primary key for that table.
At the same time, when a user enters the e-mail address, you'd be making a HTTP request to a php file on your web-server to handle sending the e-mail with the token/link to that particular user.
HTTP information.
When the user clicks the address with the token, the web server handles to set the verified e-mail player variable in the database to true, marking the user as verified. Make sure you settup a database user for the website that only has access to that particular action and none other so that if your web-server gets hi-jacked, the db user won't be able to do much in the samp server itself.
Created_At is included in case you want to place a time limit on the lifetime of the token.
Good luck.
Edit: Forgot to mention that when the user clicks on the link from the e-mail address, your php code would need to query the EmailTokens table and crosscheck the given token with the matched one from that table (if it's valid). If there's a match, you can check wether or not it's expired using the Created_At datetime/timestamp and also find that particual user that the token is refeering to using the userID.