Add in your gemfile:
gem 'validates_email_format_of'
and in your model:
validates :email, email_format: { message: "doesn't look like an email address" }
Or if you don't want use a gem, use regex:
validates_format_of :email, :with => /A([^@s]+)@((?:[-a-z0-9]+.)+[a-z]{2,})z/i
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