app/views/devise/mailer/email_changed.html.erb
<p><%= t('devise.mailer.email_changed.hello') %> <%= @email %>!</p>
<% if @resource.try(:unconfirmed_email?) %>
<p><%= t('devise.mailer.email_changed.email_is_being_changed') %> <%= @resource.unconfirmed_email %>.</p>
<% else %>
<p><%= t('devise.mailer.email_changed.email_has_been_changed') %> <%= @resource.email %>.</p>
<% end %>