diff --git a/Gemfile.lock b/Gemfile.lock
index 4315467..b52f080 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    effective_mailchimp (0.13.0)
+    effective_mailchimp (0.13.2)
       MailchimpMarketing
       effective_bootstrap
       effective_datatables (>= 4.0.0)
@@ -391,7 +391,6 @@ DEPENDENCIES
   effective_test_bot
   haml-rails
   pry-byebug
-  psych
   sqlite3
   wicked
 
diff --git a/app/models/effective/mailchimp_api.rb b/app/models/effective/mailchimp_api.rb
index 8476ba1..e128fec 100644
--- a/app/models/effective/mailchimp_api.rb
+++ b/app/models/effective/mailchimp_api.rb
@@ -3,6 +3,7 @@
 # https://mailchimp.com/developer/marketing/api/
 
 require 'MailchimpMarketing'
+require 'digest'
 
 module Effective
   class MailchimpApi
@@ -75,14 +76,14 @@ def list(id)
     def categories(list_id)
       Rails.logger.info "[effective_mailchimp] Index Interest Categories" if debug?
 
-      response = client.lists.get_list_interest_categories(list_id.try(:mailchimp_id) || list_id)
+      response = client.lists.get_list_interest_categories(list_id.try(:mailchimp_id) || list_id, count: 1000)
       Array(response['categories']) - [nil, '', {}]
     end
 
     def interests(list_id, category_id)
       Rails.logger.info "[effective_mailchimp] Index Interest Category Interests" if debug?
 
-      response = client.lists.list_interest_category_interests(list_id, category_id)
+      response = client.lists.list_interest_category_interests(list_id, category_id, count: 1000)
       Array(response['interests']) - [nil, '', {}]
     end
 
@@ -92,7 +93,7 @@ def list_member(id, email)
       Rails.logger.info "[effective_mailchimp] Get List Member" if debug?
 
       begin
-        client.lists.get_list_member(id.try(:mailchimp_id) || id, email)
+        client.lists.get_list_member(id.try(:mailchimp_id) || id, subscriber_hash(email))
       rescue MailchimpMarketing::ApiError => e
         {}
       end
@@ -127,9 +128,9 @@ def list_member_add(member)
       Rails.logger.info "[effective_mailchimp] Add List Member" if debug?
       return if sandbox_mode?
 
-      # Actually add or update
-      payload = list_member_payload(member)
-      client.lists.set_list_member(member.mailchimp_list.mailchimp_id, member.email, payload)
+      # Actually add or update. set_list_member applies status_if_new when the contact is new
+      payload = list_member_payload(member).merge(status_if_new: list_member_status(member))
+      client.lists.set_list_member(member.mailchimp_list.mailchimp_id, subscriber_hash(member.user.email), payload)
     end
 
     def list_member_update(member)
@@ -139,7 +140,8 @@ def list_member_update(member)
       return if sandbox_mode?
 
       payload = list_member_payload(member)
-      client.lists.update_list_member(member.mailchimp_list.mailchimp_id, member.email, payload)
+      hash = member.mailchimp_id.presence || subscriber_hash(member.email)
+      client.lists.update_list_member(member.mailchimp_list.mailchimp_id, hash, payload)
     end
 
     def list_member_payload(member)
@@ -150,11 +152,22 @@ def list_member_payload(member)
 
       payload = {
         email_address: member.user.email,
-        status: (member.subscribed ? 'subscribed' : 'unsubscribed'),
+        status: list_member_status(member),
         merge_fields: merge_fields.transform_values { |value| value || '' },
         interests: member.interests_hash.presence
       }.compact
     end
 
+    # Mailchimp identifies a list member by the MD5 hash of their lowercase email address
+    def subscriber_hash(email)
+      raise('expected an email') unless email.to_s.include?('@')
+
+      Digest::MD5.hexdigest(email.to_s.downcase.strip)
+    end
+
+    def list_member_status(member)
+      member.subscribed ? 'subscribed' : 'unsubscribed'
+    end
+
   end
 end
diff --git a/test/models/mailchimp_api_test.rb b/test/models/mailchimp_api_test.rb
new file mode 100644
index 0000000..3572bc8
--- /dev/null
+++ b/test/models/mailchimp_api_test.rb
@@ -0,0 +1,24 @@
+require 'test_helper'
+
+class MailchimpApiTest < ActiveSupport::TestCase
+  def api
+    @api ||= Effective::MailchimpApi.new(api_key: 'test-us1')
+  end
+
+  test 'subscriber_hash is the md5 of the lowercase email' do
+    expected = Digest::MD5.hexdigest('brenda.barrera@quadreal.com')
+
+    assert_equal expected, api.subscriber_hash('brenda.barrera@quadreal.com')
+  end
+
+  test 'subscriber_hash lowercases and strips before hashing' do
+    expected = Digest::MD5.hexdigest('brenda.barrera@quadreal.com')
+
+    assert_equal expected, api.subscriber_hash('  Brenda.Barrera@QuadReal.com  ')
+  end
+
+  test 'subscriber_hash raises without an email' do
+    assert_raises(RuntimeError) { api.subscriber_hash('not-an-email') }
+  end
+
+end