Install rails_admin and devise. Start setting it up.

app/views/devise/mailer/confirmation_instructions.html.erb

@@ -0,0 +1,5 @@
+<p>Welcome <%= @email %>!</p>
+
+<p>You can confirm your account email through the link below:</p>
+
+<p><%= link_to 'Confirm my account', confirmation_url(@resource, confirmation_token: @token) %></p>

app/views/devise/mailer/email_changed.html.erb

@@ -0,0 +1,7 @@
+<p>Hello <%= @email %>!</p>
+
+<% if @resource.try(:unconfirmed_email?) %>
+  <p>We're contacting you to notify you that your email is being changed to <%= @resource.unconfirmed_email %>.</p>
+<% else %>
+  <p>We're contacting you to notify you that your email has been changed to <%= @resource.email %>.</p>
+<% end %>

app/views/devise/mailer/password_change.html.erb

@@ -0,0 +1,3 @@
+<p>Hello <%= @resource.email %>!</p>
+
+<p>We're contacting you to notify you that your password has been changed.</p>

app/views/devise/mailer/reset_password_instructions.html.erb

@@ -0,0 +1,8 @@
+<p>Hello <%= @resource.email %>!</p>
+
+<p>Someone has requested a link to change your password. You can do this through the link below.</p>
+
+<p><%= link_to 'Change my password', edit_password_url(@resource, reset_password_token: @token) %></p>
+
+<p>If you didn't request this, please ignore this email.</p>
+<p>Your password won't change until you access the link above and create a new one.</p>

app/views/devise/mailer/unlock_instructions.html.erb

@@ -0,0 +1,7 @@
+<p>Hello <%= @resource.email %>!</p>
+
+<p>Your account has been locked due to an excessive number of unsuccessful sign in attempts.</p>
+
+<p>Click the link below to unlock your account:</p>
+
+<p><%= link_to 'Unlock my account', unlock_url(@resource, unlock_token: @token) %></p>