diff --git a/Gemfile b/Gemfile
index 6085dc1c..1353899d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -221,6 +221,9 @@ gem 'dalli'
 
 gem 'icalendar'
 
+# for making external requests easier
+gem 'httparty'
+
 # pagination
 gem 'pagy', '<4.0'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 9515baf8..68d93759 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -715,6 +715,7 @@ DEPENDENCIES
   guard-rspec
   haml-lint
   haml-rails
+  httparty
   icalendar
   iso-639
   jquery-datatables
diff --git a/app/controllers/conference_registrations_controller.rb b/app/controllers/conference_registrations_controller.rb
index 8d4ae8a1..6a64ff8a 100644
--- a/app/controllers/conference_registrations_controller.rb
+++ b/app/controllers/conference_registrations_controller.rb
@@ -57,6 +57,8 @@ class ConferenceRegistrationsController < ApplicationController
         sign_in(@registration.user)
       end
 
+      MailblusterEditLeadJob.perform_later(@user, add_tags: ["snapcon-#{@conference.short_title}"])
+
       if @conference.tickets.visible.any? && !current_user.supports?(@conference)
         redirect_to conference_tickets_path(@conference.short_title),
                     notice: 'You are now registered and will be receiving E-Mail notifications.'
@@ -87,6 +89,7 @@ class ConferenceRegistrationsController < ApplicationController
 
   def destroy
     if @registration.destroy
+      MailblusterEditLeadJob.perform_later(@user, remove_tags: ["snapcon-#{@conference.short_title}"])
       redirect_to root_path,
                   notice: "You are not registered for #{@conference.title} anymore!"
     else
diff --git a/app/jobs/mailbluster_create_lead_job.rb b/app/jobs/mailbluster_create_lead_job.rb
new file mode 100644
index 00000000..701719d7
--- /dev/null
+++ b/app/jobs/mailbluster_create_lead_job.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class MailblusterCreateLeadJob < ApplicationJob
+  queue_as :default
+
+  def perform(user)
+    MailblusterManager.create_lead(user)
+  end
+end
diff --git a/app/jobs/mailbluster_delete_lead_job.rb b/app/jobs/mailbluster_delete_lead_job.rb
new file mode 100644
index 00000000..387d1cc0
--- /dev/null
+++ b/app/jobs/mailbluster_delete_lead_job.rb
@@ -0,0 +1,7 @@
+class MailblusterDeleteLeadJob < ApplicationJob
+  queue_as :default
+
+  def perform(user)
+    MailblusterManager.delete_lead(user)
+  end
+end
diff --git a/app/jobs/mailbluster_edit_lead_job.rb b/app/jobs/mailbluster_edit_lead_job.rb
new file mode 100644
index 00000000..ff5d07ce
--- /dev/null
+++ b/app/jobs/mailbluster_edit_lead_job.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class MailblusterEditLeadJob < ApplicationJob
+  queue_as :default
+
+  def perform(user, add_tags: [], remove_tags: [], old_email: nil)
+    MailblusterManager.edit_lead(user, add_tags: add_tags, remove_tags: remove_tags, old_email: old_email)
+  end
+end
diff --git a/app/models/concerns/track_saved_changes.rb b/app/models/concerns/track_saved_changes.rb
new file mode 100644
index 00000000..db75e625
--- /dev/null
+++ b/app/models/concerns/track_saved_changes.rb
@@ -0,0 +1,48 @@
+# https://github.com/ccmcbeck/after-commit
+module TrackSavedChanges
+  extend ActiveSupport::Concern
+
+  included do
+    # expose the details if consumer wants to do more
+    # attr_reader :ts_saved_changes_history, :ts_saved_changes_unfiltered
+    after_initialize :ts_reset_saved_changes
+    after_save :ts_track_saved_changes
+  end
+
+  # on initalize, but useful for fine grain control
+  def ts_reset_saved_changes
+    @ts_saved_changes_unfiltered = {}
+    @ts_saved_changes_history = []
+  end
+
+  # filter out any changes that result in the original value
+  def ts_saved_changes
+    @ts_saved_changes_unfiltered.reject { |_k, v| v[0] == v[1] }
+  end
+
+  private
+
+  # on save
+  def ts_track_saved_changes
+    # maintain an array of ActiveModel::Dirty.changes
+    @ts_saved_changes_history << previous_changes.dup
+    # accumulate the most recent changes
+    @ts_saved_changes_history.last.each_pair { |k, v| ts_track_saved_change k, v }
+  end
+
+  # v is an an array of [prev, current]
+  def ts_track_saved_change(key, value)
+    if @ts_saved_changes_unfiltered.key? key
+      @ts_saved_changes_unfiltered[key][1] = ts_track_saved_value value[1]
+    else
+      @ts_saved_changes_unfiltered[key] = value.dup
+    end
+  end
+
+  # type safe dup inspred by http://stackoverflow.com/a/20955038
+  def ts_track_saved_value(value)
+    value.dup
+  rescue TypeError
+    value
+  end
+end
diff --git a/app/models/user.rb b/app/models/user.rb
index 955c76d1..ddcf63bb 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -53,6 +53,7 @@ class UserDisabled < StandardError
 end
 
 class User < ApplicationRecord
+  include TrackSavedChanges
   rolify
   # prevent N+1 queries with has_cached_role? by preloading roles *always*
   default_scope { preload(:roles) }
@@ -80,6 +81,12 @@ class User < ApplicationRecord
 
   after_save :touch_events
 
+  # Note that using after_create_commit and after_update_commit does not work.
+  # See https://github.com/CactusPuppy/snapcon/pull/43#discussion_r609458034
+  after_commit :mailbluster_create_lead, on: :create
+  after_commit :mailbluster_delete_lead, on: :destroy
+  after_commit :mailbluster_update_lead, on: :update, if: ->(user){ ['name', 'email'].any? { |key| user.ts_saved_changes.key? key } }
+
   # add scope
   scope :comment_notifiable, ->(conference) {joins(:roles).where('roles.name IN (?)', [:organizer, :cfp]).where('roles.resource_type = ? AND roles.resource_id = ?', 'Conference', conference.id)}
 
@@ -361,12 +368,32 @@ class User < ApplicationRecord
     User.count == 1 && User.first.email == 'deleted@localhost.osem'
   end
 
+  # TODO: email_hash function for mailbluster
+  # def email_hash
+  #   Digest::MD5.hexdigest user.email
+  # end
+
   private
 
   def setup_role
     self.is_admin = true if User.empty?
   end
 
+  def mailbluster_create_lead
+    MailblusterCreateLeadJob.perform_later self
+    ts_reset_saved_changes
+  end
+
+  def mailbluster_delete_lead
+    MailblusterDeleteLeadJob.perform_later email
+    ts_reset_saved_changes
+  end
+
+  def mailbluster_update_lead
+    MailblusterEditLeadJob.perform_later(self, old_email: ts_saved_changes.fetch('email', [nil])[0])
+    ts_reset_saved_changes
+  end
+
   def touch_events
     event_users.each(&:touch)
   end
diff --git a/app/services/mailbluster_manager.rb b/app/services/mailbluster_manager.rb
new file mode 100644
index 00000000..d74ea76a
--- /dev/null
+++ b/app/services/mailbluster_manager.rb
@@ -0,0 +1,40 @@
+class MailblusterManager
+  include HTTParty
+  base_uri 'https://api.mailbluster.com/api/leads/'
+  @auth_headers = {
+    headers: {
+      'Content-Type'  => 'application/json',
+      'Authorization' => ENV['MAILBLUSTER_API_KEY']
+    }
+  }
+
+  def self.query_api(method, path, body: {})
+    options = @auth_headers.merge(body: body.to_json)
+    send(method, path, options).parsed_response
+  end
+
+  def self.create_lead(user)
+    query_api(:post, '/', body: {
+                'email'            => user.email,
+                'firstName'        => user.name,
+                'overrideExisting' => true,
+                'subscribed'       => true,
+                'tags'             => [ENV['OSEM_NAME'] || 'snapcon']
+              })
+  end
+
+  def self.edit_lead(user, add_tags: [], remove_tags: [], old_email: nil)
+    email_hash = Digest::MD5.hexdigest(old_email.presence || user.email)
+    query_api(:put, "/#{email_hash}", body: {
+                'email'      => user.email,
+                'firstName'  => user.name,
+                'addTags'    => add_tags,
+                'removeTags' => remove_tags
+              })
+  end
+
+  def self.delete_lead(email)
+    email_hash = Digest::MD5.hexdigest email
+    query_api(:delete, "/#{email_hash}")
+  end
+end
diff --git a/spec/factories/users.rb b/spec/factories/users.rb
index fcec2048..75af7370 100644
--- a/spec/factories/users.rb
+++ b/spec/factories/users.rb
@@ -80,8 +80,30 @@ FactoryBot.define do
     last_sign_in_at { Date.today }
     is_disabled { false }
 
+    after(:build) do |user|
+      url_mailbluster = 'https://api.mailbluster.com/api/leads/'
+      response_body = "{
+        \"message\": \"Lead created\",
+        \"lead\": {
+          \"id\": 329395,
+          \"firstName\": \"#{user.name}\",
+          \"lastName\": \"\",
+          \"fullName\": \"#{user.name}\",
+          \"email\": \"#{user.email}\",
+          \"subscribed\": true,
+          \"tags\": [
+            #{ENV['OSEM_NAME'] || 'snapcon'}
+          ],
+        }
+      }"
+      WebMock.stub_request(:post, url_mailbluster)
+        .to_return(body: response_body, status: 200)
+    end
+    # Called by every user creation
+
     after(:create) do |user|
       user.is_admin = false
+
       # save with bang cause we want change in DB and not just in object instance
       user.save!
     end
diff --git a/spec/services/mailbluster_manager_spec.rb b/spec/services/mailbluster_manager_spec.rb
new file mode 100644
index 00000000..52851089
--- /dev/null
+++ b/spec/services/mailbluster_manager_spec.rb
@@ -0,0 +1,140 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require 'webmock/rspec'
+
+describe MailblusterManager, type: :model do
+  let!(:user) { create(:user) }
+
+  before(:each) do
+    WebMock.reset_executed_requests!
+  end
+
+  url = 'https://api.mailbluster.com/api/leads/'
+
+  describe 'query_api' do
+    it 'translates :get to a get request' do
+      stub_request(:get, url)
+      described_class.query_api(:get, '/')
+
+      expect(WebMock).to have_requested(:get, url)
+    end
+
+    it 'translates :post to a post request' do
+      stub_request(:post, url + 'path')
+      described_class.query_api(:post, '/path', body: { key: 'value' })
+
+      expect(WebMock).to have_requested(:post, url + 'path').with(body: { key: 'value' })
+    end
+  end
+
+  describe 'create_lead' do
+    it 'makes a post request to Mailbluster\'s API and gets the correct response' do
+      response_body = "{
+        \"message\": \"Lead created\",
+        \"lead\": {
+          \"id\": 329395,
+          \"firstName\": \"#{user.name}\",
+          \"lastName\": \"\",
+          \"fullName\": \"#{user.name}\",
+          \"email\": \"#{user.email}\",
+          \"subscribed\": true,
+          \"tags\": [
+            #{ENV['OSEM_NAME'] || 'snapcon'}
+          ],
+        }
+      }"
+      stub_request(:post, url)
+        .to_return(body: response_body, status: 200)
+      response = described_class.create_lead(user)
+
+      expect(WebMock).to have_requested(:post, url).with(body: {
+        'email':            user.email,
+        'firstName':        user.name,
+        'overrideExisting': true,
+        'subscribed':       true,
+        'tags':             [ENV['OSEM_NAME'] || 'snapcon']
+      }.to_json)
+      expect(response).to eq(response_body)
+    end
+  end
+
+  describe 'edit_lead' do
+    it 'makes a put request to Mailbluster\'s API to change the email and gets the correct response' do
+      response_body = "{
+        \"message\": \"Lead updated\",
+        \"lead\": {
+          \"id\": 329395,
+          \"firstName\": \"#{user.name}\",
+          \"lastName\": \"\",
+          \"fullName\": \"#{user.name}\",
+          \"email\": \"#{user.email}\",
+          \"subscribed\": true,
+          \"tags\": [
+            #{ENV['OSEM_NAME'] || 'snapcon'}
+          ],
+        }
+      }"
+      old_email = user.email
+      user.email = 'new@new.org'
+      user.save
+      stub_request(:put, url + Digest::MD5.hexdigest(old_email))
+        .to_return(body: response_body, status: 200)
+      response = described_class.edit_lead(user, old_email: old_email)
+
+      expect(WebMock).to have_requested(:put, url + Digest::MD5.hexdigest(old_email)).with(body: {
+        'email':      user.email,
+        'firstName':  user.name,
+        'addTags':    [],
+        'removeTags': []
+      }.to_json)
+      expect(response).to eq(response_body)
+    end
+
+    it 'makes a put request to Mailbluster\'s API to add a tag and gets the correct response' do
+      response_body = "{
+        \"message\": \"Lead updated\",
+        \"lead\": {
+          \"id\": 329395,
+          \"firstName\": \"#{user.name}\",
+          \"lastName\": \"\",
+          \"fullName\": \"#{user.name}\",
+          \"email\": \"#{user.email}\",
+          \"subscribed\": true,
+          \"tags\": [
+            #{ENV['OSEM_NAME'] || 'snapcon'}, '2021'
+          ],
+        }
+      }"
+      stub_request(:put, url + Digest::MD5.hexdigest(user.email))
+        .to_return(body: response_body, status: 200)
+      add_tags = ['2021']
+      response = described_class.edit_lead(user, add_tags: add_tags)
+
+      expect(WebMock).to have_requested(:put, url + Digest::MD5.hexdigest(user.email)).with(body: {
+        'email':      user.email,
+        'firstName':  user.name,
+        'addTags':    add_tags,
+        'removeTags': []
+      }.to_json)
+      expect(response).to eq(response_body)
+    end
+  end
+
+  describe 'delete_lead' do
+    it 'correctly requests the right URL and gets a valid response' do
+      email_hash = Digest::MD5.hexdigest user.email
+      response_body = "{
+        \"message\":\"Lead deleted\",
+        \"leadHash\":\"#{email_hash}\"
+      }"
+      lead_url = url + email_hash.to_s
+      stub_request(:delete, lead_url)
+        .to_return(body: response_body)
+      response = described_class.delete_lead(user.email)
+
+      expect(WebMock).to have_requested(:delete, lead_url)
+      expect(response).to eq(response_body)
+    end
+  end
+end
diff --git a/spec/support/external_request.rb b/spec/support/external_request.rb
index c968acd3..fbedd9e3 100644
--- a/spec/support/external_request.rb
+++ b/spec/support/external_request.rb
@@ -11,6 +11,7 @@ RSpec.configure do |config|
   config.before(:each) do
     mock_commercial_request
     mock_image_request
+    mock_default_mailbluster
   end
 end
 
@@ -39,3 +40,7 @@ def mock_image_request
   WebMock.stub_request(:post, 'https://api.cloudinary.com/v1_1/snapcon/image/destroy')
     .to_return(status: 200, body: {}.to_json, headers: {})
 end
+
+def mock_default_mailbluster
+  WebMock.stub_request(:any, /api.mailbluster.com/)
+end