how to block specific mail servers

[ShMilO]

recently i noticed that there are more and more fake mails
that allow a user to make a mail without registering to it
unlike gmail from example

so is there an option for me to block those mails from registering

if so will it affect existing members ?

thanks in advance

[Trevor Hannant]

AdminCP > vBulletin Options > User Banning Options > Banned Email Addresses