diff --git a/app/jobs/handle_email_signin_job.rb b/app/jobs/handle_email_signin_job.rb
index 4f111f4..0f45b32 100644
--- a/app/jobs/handle_email_signin_job.rb
+++ b/app/jobs/handle_email_signin_job.rb
@@ -5,7 +5,7 @@ class HandleEmailSigninJob < ApplicationJob
     email_address = ActiveRecord::Base.transaction do
       EmailAddress.find_by(email: email) || begin
         user = User.create!
-        user.email_addresses.create!(email: email, source: :direct)
+        user.email_addresses.create!(email: email, source: :signing_in)
       end
     end
 
diff --git a/app/jobs/one_time/backfill_email_sources_job.rb b/app/jobs/one_time/backfill_email_sources_job.rb
new file mode 100644
index 0000000..c953950
--- /dev/null
+++ b/app/jobs/one_time/backfill_email_sources_job.rb
@@ -0,0 +1,38 @@
+class OneTime::BackfillEmailSourcesJob < ApplicationJob
+  queue_as :default
+
+  def perform
+    # Backfill email addresses from Slack
+
+    users.find_each do |user|
+      slack_user_info = user.raw_slack_user_info
+      github_user_info = user.raw_github_user_info
+      sleep 1
+
+      user.email_addresses.where(source: nil).each do |email_address|
+        puts "Checking #{email_address.email} for #{user.id}"
+        if slack_user_info&.dig("user", "profile", "email") == email_address.email
+          email_address.update!(source: :slack)
+          puts "Updated #{email_address.email} for #{user.id} to slack"
+        elsif github_user_info&.dig("email") == email_address.email
+          email_address.update!(source: :github)
+          puts "Updated #{email_address.email} for #{user.id} to github"
+        end
+      end
+
+      other_addresses = user.email_addresses.where(source: nil)
+      if other_addresses.any?
+        puts "Updating #{other_addresses.count} email addresses for #{user.id} to direct"
+        other_addresses.update_all(source: :signing_in)
+      end
+    end
+  end
+
+  private
+
+  def users
+    # any user with email addresses that don't have a source
+    @users ||= User.includes(:email_addresses)
+                   .where(email_addresses: { source: nil })
+  end
+end
diff --git a/app/models/email_address.rb b/app/models/email_address.rb
index 5c383c9..551a752 100644
--- a/app/models/email_address.rb
+++ b/app/models/email_address.rb
@@ -6,7 +6,7 @@ class EmailAddress < ApplicationRecord
                    format: { with: URI::MailTo::EMAIL_REGEXP }
 
   enum :source, {
-    direct: 0,
+    signing_in: 0,
     github: 1,
     slack: 2
   }, prefix: true
diff --git a/app/models/user.rb b/app/models/user.rb
index 65efa60..446ffe2 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -96,6 +96,16 @@ class User < ApplicationRecord
     update!(is_admin: false)
   end
 
+  def raw_github_user_info
+    return nil unless github_uid.present?
+    return nil unless github_access_token.present?
+
+    @github_user_info ||= HTTP.auth("Bearer #{github_access_token}")
+      .get("https://api.github.com/user")
+
+    JSON.parse(@github_user_info.body.to_s)
+  end
+
   def raw_slack_user_info
     return nil unless slack_uid.present?
     return nil unless slack_access_token.present?
diff --git a/app/views/users/edit.html.erb b/app/views/users/edit.html.erb
index 18c2b14..3d02633 100644
--- a/app/views/users/edit.html.erb
+++ b/app/views/users/edit.html.erb
@@ -91,7 +91,14 @@
     <% if @user.email_addresses.any? %>
       <ul>
         <% @user.email_addresses.each do |email_address| %>
-          <li><%= email_address.email %></li>
+          <li>
+            <%= email_address.email %>
+            <% if email_address.source.present? %>
+              <span class="super">
+                (from <%= email_address.source.humanize %>)
+              </span>
+            <% end %>
+          </li>
         <% end %>
       </ul>
     <% else %>