diff --git a/app/controllers/account/organisations_controller.rb b/app/controllers/account/organisations_controller.rb
index 30d215e0c2..6eb3908b35 100644
--- a/app/controllers/account/organisations_controller.rb
+++ b/app/controllers/account/organisations_controller.rb
@@ -6,6 +6,13 @@ class OrganisationsController < WebController
     skip_before_action :redirect_if_account_not_completed
 
     def edit
+      @organisations = Organisation.for_email(current_user.email).order(:name)
+
+      if @organisations.empty?
+        render :unsupported_email
+        return
+      end
+
       @organisation_input = OrganisationInput.new(user: current_user).assign_form_values
     end
 
diff --git a/app/models/org_domain.rb b/app/models/org_domain.rb
new file mode 100644
index 0000000000..aa966f2d49
--- /dev/null
+++ b/app/models/org_domain.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class OrgDomain < ApplicationRecord
+  belongs_to :organisation
+
+  validates :domain, presence: true
+  validates :domain, uniqueness: { scope: :organisation_id, case_sensitive: false }
+
+  before_validation -> { self.domain = domain&.downcase&.strip }
+end
diff --git a/app/models/organisation.rb b/app/models/organisation.rb
index 1209911eee..ada22dcb8a 100644
--- a/app/models/organisation.rb
+++ b/app/models/organisation.rb
@@ -4,6 +4,7 @@ class Organisation < ApplicationRecord
   has_many :groups
   has_many :users
 
+  has_many :org_domains, dependent: :destroy
   has_many :mou_signatures
 
   scope :not_closed, -> { where(closed: false) }
@@ -28,4 +29,13 @@ def as_json(options = {})
     options[:methods] ||= %i[organisation_admin_users]
     super(options)
   end
+
+  def self.for_email(email)
+    domain = email.split('@').last.downcase
+
+    not_closed
+      .joins(:org_domains)
+      .where(org_domains: { domain: domain })
+      .distinct
+  end
 end
diff --git a/app/views/account/organisations/edit.html.erb b/app/views/account/organisations/edit.html.erb
index 66261814e3..33560477e0 100644
--- a/app/views/account/organisations/edit.html.erb
+++ b/app/views/account/organisations/edit.html.erb
@@ -10,7 +10,7 @@
         f,
         attribute_name: :organisation_id,
         form_field: f.govuk_collection_select(:organisation_id,
-                                              Organisation.not_closed.order(:name),
+                                              @organisations,
                                               :id,
                                               :name_with_abbreviation,
                                               class: ['govuk-!-width-three-quarters'],
diff --git a/app/views/account/organisations/unsupported_email.html.erb b/app/views/account/organisations/unsupported_email.html.erb
new file mode 100644
index 0000000000..55e76ac700
--- /dev/null
+++ b/app/views/account/organisations/unsupported_email.html.erb
@@ -0,0 +1,9 @@
+<div class="govuk-grid-row">
+  <div class="govuk-grid-column-two-thirds">
+    <h1 class="govuk-heading-l">We do not recognise your email address</h1>
+    <p class="govuk-body">
+      Your email address (<%= current_user.email %>) is not associated with a supported organisation.
+    </p>
+    <%= govuk_details(summary_text: t('account.organisation_details_summary'), text: t('account.organisation_text_html', contact_link: contact_link)) %>
+  </div>
+</div>
diff --git a/db/migrate/20260622151619_create_org_domains.rb b/db/migrate/20260622151619_create_org_domains.rb
new file mode 100644
index 0000000000..ff0902bcdd
--- /dev/null
+++ b/db/migrate/20260622151619_create_org_domains.rb
@@ -0,0 +1,12 @@
+class CreateOrgDomains < ActiveRecord::Migration[8.1]
+  def change
+    create_table :org_domains do |t|
+      t.references :organisation, null: false, foreign_key: true
+      t.string :domain, null: false
+      t.timestamps
+    end
+
+    add_index :org_domains, [:organisation_id, :domain], unique: true, name: "index_org_domains_unique"
+    add_index :org_domains, :domain
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index f9401740c5..1aee24074d 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_06_08_112508) do
+ActiveRecord::Schema[8.1].define(version: 2026_06_22_151619) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -199,6 +199,16 @@
     t.index ["user_id"], name: "index_mou_signatures_on_user_id_unique_without_organisation_id", unique: true, where: "(organisation_id IS NULL)", comment: "Users can only sign a single MOU without an organisation"
   end
 
+  create_table "org_domains", force: :cascade do |t|
+    t.datetime "created_at", null: false
+    t.string "domain", null: false
+    t.bigint "organisation_id", null: false
+    t.datetime "updated_at", null: false
+    t.index ["domain"], name: "index_org_domains_on_domain"
+    t.index ["organisation_id", "domain"], name: "index_org_domains_unique", unique: true
+    t.index ["organisation_id"], name: "index_org_domains_on_organisation_id"
+  end
+
   create_table "organisations", force: :cascade do |t|
     t.string "abbreviation"
     t.boolean "closed", default: false
@@ -297,6 +307,7 @@
   add_foreign_key "memberships", "users", column: "added_by_id"
   add_foreign_key "mou_signatures", "organisations"
   add_foreign_key "mou_signatures", "users"
+  add_foreign_key "org_domains", "organisations"
   add_foreign_key "page_translations", "pages"
   add_foreign_key "pages", "forms"
   add_foreign_key "users", "organisations"