diff --git a/app/mailers/user_mailer.rb b/app/mailers/user_mailer.rb
index 3cfc95c9..1bc42c89 100644
--- a/app/mailers/user_mailer.rb
+++ b/app/mailers/user_mailer.rb
@@ -23,7 +23,7 @@ class UserMailer < ApplicationMailer
     token = AuthenticationToken.generate!(request_for_comment.user)
     @receiver_displayname = request_for_comment.user.displayname
     @commenting_user_displayname = commenting_user.displayname
-    @comment_text = comment.text
+    @comment_text = ERB::Util.html_escape comment.text
     @rfc_link = request_for_comment_url(request_for_comment, token: token.shared_secret)
     mail(
       subject: t('mailers.user_mailer.got_new_comment.subject',
@@ -35,7 +35,7 @@ class UserMailer < ApplicationMailer
     token = AuthenticationToken.generate!(subscription.user)
     @receiver_displayname = subscription.user.displayname
     @author_displayname = from_user.displayname
-    @comment_text = comment.text
+    @comment_text = ERB::Util.html_escape comment.text
     @rfc_link = request_for_comment_url(subscription.request_for_comment, token: token.shared_secret)
     @unsubscribe_link = unsubscribe_subscription_url(subscription)
     mail(
@@ -48,7 +48,7 @@ class UserMailer < ApplicationMailer
     token = AuthenticationToken.generate!(receiver)
     @receiver_displayname = receiver.displayname
     @author = request_for_comment.user.displayname
-    @thank_you_note = request_for_comment.thank_you_note
+    @thank_you_note = ERB::Util.html_escape request_for_comment.thank_you_note
     @rfc_link = request_for_comment_url(request_for_comment, token: token.shared_secret)
     mail(subject: t('mailers.user_mailer.send_thank_you_note.subject', author: @author), to: receiver.email)
   end
diff --git a/spec/mailers/user_mailer_spec.rb b/spec/mailers/user_mailer_spec.rb
index 7f5ae70b..ace8f719 100644
--- a/spec/mailers/user_mailer_spec.rb
+++ b/spec/mailers/user_mailer_spec.rb
@@ -93,6 +93,25 @@ describe UserMailer do
       # A five minute tolerance is allowed to account for the time difference between `now` and the creation timestamp of the token.
       expect(token.expire_at - Time.zone.now).to be_within(5.minutes).of(7.days)
     end
+
+    it 'sets the correct comment' do
+      expect(mail.body).to include(request_for_comment.comments.first.text)
+    end
+
+    context 'with an HTML comment' do
+      let(:html_comment) { '<b>test</b>' }
+      let(:escaped_comment) { '&lt;b&gt;test&lt;/b&gt;' }
+
+      before { request_for_comment.comments.first.update(text: html_comment) }
+
+      it 'does not include the HTML tags' do
+        expect(mail.body).not_to include(html_comment)
+      end
+
+      it 'includes escaped HTML tags' do
+        expect(mail.body).to include(escaped_comment)
+      end
+    end
   end
 
   describe '#got_new_comment_for_subscription' do
@@ -128,21 +147,41 @@ describe UserMailer do
       # A five minute tolerance is allowed to account for the time difference between `now` and the creation timestamp of the token.
       expect(token.expire_at - Time.zone.now).to be_within(5.minutes).of(7.days)
     end
+
+
+    it 'sets the correct comment' do
+      expect(mail.body).to include(request_for_comment.comments.first.text)
+    end
+
+    context 'with an HTML comment' do
+      let(:html_comment) { '<b>test</b>' }
+      let(:escaped_comment) { '&lt;b&gt;test&lt;/b&gt;' }
+
+      before { request_for_comment.comments.first.update(text: html_comment) }
+
+      it 'does not include the HTML tags' do
+        expect(mail.body).not_to include(html_comment)
+      end
+
+      it 'includes escaped HTML tags' do
+        expect(mail.body).to include(escaped_comment)
+      end
+    end
   end
 
   describe '#send_thank_you_note' do
     let(:user) { create(:learner) }
     let(:receiver) { create(:teacher) }
     let(:token) { AuthenticationToken.find_by(user: receiver) }
-    let(:request_for_comments) { create(:rfc_with_comment, user: user) }
-    let(:mail) { described_class.send_thank_you_note(request_for_comments, receiver).deliver_now }
+    let(:request_for_comment) { create(:rfc_with_comment, user: user) }
+    let(:mail) { described_class.send_thank_you_note(request_for_comment, receiver).deliver_now }
 
     it 'sets the correct sender' do
       expect(mail.from).to include('codeocean@hpi.de')
     end
 
     it 'sets the correct subject' do
-      expect(mail.subject).to eq(I18n.t('mailers.user_mailer.send_thank_you_note.subject', author: request_for_comments.user.displayname))
+      expect(mail.subject).to eq(I18n.t('mailers.user_mailer.send_thank_you_note.subject', author: request_for_comment.user.displayname))
     end
 
     it 'sets the correct receiver' do
@@ -150,7 +189,7 @@ describe UserMailer do
     end
 
     it 'includes the correct URL' do
-      expect(mail.body).to include(request_for_comment_url(request_for_comments, token: token.shared_secret))
+      expect(mail.body).to include(request_for_comment_url(request_for_comment, token: token.shared_secret))
     end
 
     it 'creates a new authentication token' do
@@ -162,5 +201,25 @@ describe UserMailer do
       # A five minute tolerance is allowed to account for the time difference between `now` and the creation timestamp of the token.
       expect(token.expire_at - Time.zone.now).to be_within(5.minutes).of(7.days)
     end
+
+
+    it 'sets the correct thank_you_note' do
+      expect(mail.body).to include(request_for_comment.thank_you_note)
+    end
+
+    context 'with an HTML comment' do
+      let(:html_comment) { '<b>test</b>' }
+      let(:escaped_comment) { '&lt;b&gt;test&lt;/b&gt;' }
+
+      before { request_for_comment.update(thank_you_note: html_comment) }
+
+      it 'does not include the HTML tags' do
+        expect(mail.body).not_to include(html_comment)
+      end
+
+      it 'includes escaped HTML tags' do
+        expect(mail.body).to include(escaped_comment)
+      end
+    end
   end
 end