diff --git a/.rubocop/todo.rspec.yml b/.rubocop/todo.rspec.yml
index 0c376cbea..1729baba2 100644
--- a/.rubocop/todo.rspec.yml
+++ b/.rubocop/todo.rspec.yml
@@ -272,7 +272,7 @@ RSpec/ExampleLength:
     - 'spec/models/trigger_spec.rb'
     - 'spec/models/user_spec.rb'
     - 'spec/requests/admin/knowledge_base/public_menu_spec.rb'
-    - 'spec/requests/api_auth_on_behalf_of_spec.rb'
+    - 'spec/requests/api_auth_from_spec.rb'
     - 'spec/requests/api_auth_spec.rb'
     - 'spec/requests/calendar_spec.rb'
     - 'spec/requests/external_credentials_spec.rb'
@@ -346,7 +346,7 @@ RSpec/InstanceVariable:
     - 'spec/lib/notification_factory/renderer_spec.rb'
     - 'spec/models/import_job_spec.rb'
     - 'spec/models/scheduler_spec.rb'
-    - 'spec/requests/api_auth_on_behalf_of_spec.rb'
+    - 'spec/requests/api_auth_from_spec.rb'
     - 'spec/requests/integration/monitoring_spec.rb'
     - 'spec/requests/integration/sipgate_spec.rb'
     - 'spec/requests/organization_spec.rb'
@@ -558,7 +558,7 @@ RSpec/MultipleExpectations:
     - 'spec/models/trigger_spec.rb'
     - 'spec/models/type_lookup_spec.rb'
     - 'spec/models/user_spec.rb'
-    - 'spec/requests/api_auth_on_behalf_of_spec.rb'
+    - 'spec/requests/api_auth_from_spec.rb'
     - 'spec/requests/api_auth_spec.rb'
     - 'spec/requests/calendar_spec.rb'
     - 'spec/requests/error_spec.rb'
diff --git a/app/controllers/application_controller/has_user.rb b/app/controllers/application_controller/has_user.rb
index 51fc9f2c6..d06e2f8b2 100644
--- a/app/controllers/application_controller/has_user.rb
+++ b/app/controllers/application_controller/has_user.rb
@@ -21,24 +21,34 @@ module ApplicationController::HasUser
     @_current_user ||= User.lookup(id: session[:user_id]) # rubocop:disable Naming/MemoizedInstanceVariableName
   end
 
+  def request_header_from
+    @request_header_from ||= begin
+      if request.headers['X-On-Behalf-Of'].present?
+        ActiveSupport::Deprecation.warn("Header 'X-On-Behalf-Of' is deprecated. Please use header 'From' instead.")
+      end
+
+      request.headers['From'] || request.headers['X-On-Behalf-Of']
+    end
+  end
+
   # Finds the user based on the id, login or email which is given
   # in the headers. If it is found then all api activities are done
   # with the behalf of user. With this functionality it is possible
   # to do changes with a user which is different from the admin user.
   # E.g. create a ticket as a customer user based on a user with admin rights.
   def current_user_on_behalf
-    return if request.headers['X-On-Behalf-Of'].blank?  # require header
+    return if request_header_from.blank? # require header
     return @_user_on_behalf if @_user_on_behalf         # return memoized user
     return if !current_user_real                        # require session user
     if !SessionsPolicy.new(current_user_real, Sessions).impersonate?
-      raise Exceptions::Forbidden, "Current user has no permission to use 'X-On-Behalf-Of'!"
+      raise Exceptions::Forbidden, "Current user has no permission to use 'From'/'X-On-Behalf-Of'!"
     end
 
-    @_user_on_behalf = find_on_behalf_user request.headers['X-On-Behalf-Of'].to_s.downcase.strip
+    @_user_on_behalf = find_on_behalf_user request_header_from.to_s.downcase.strip
 
     # no behalf of user found
     if !@_user_on_behalf
-      raise Exceptions::Forbidden, "No such user '#{request.headers['X-On-Behalf-Of']}'"
+      raise Exceptions::Forbidden, "No such user '#{request_header_from}'"
     end
 
     @_user_on_behalf
diff --git a/spec/requests/api_auth_on_behalf_of_spec.rb b/spec/requests/api_auth_from_spec.rb
similarity index 81%
rename from spec/requests/api_auth_on_behalf_of_spec.rb
rename to spec/requests/api_auth_from_spec.rb
index 17d22095c..6528dd63b 100644
--- a/spec/requests/api_auth_on_behalf_of_spec.rb
+++ b/spec/requests/api_auth_from_spec.rb
@@ -2,7 +2,7 @@
 
 require 'rails_helper'
 
-RSpec.describe 'Api Auth On Behalf Of', type: :request do
+RSpec.describe 'Api Auth From', type: :request do
 
   let(:admin) do
     create(:admin, groups: Group.all)
@@ -11,12 +11,12 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
     create(:agent)
   end
   let(:customer) do
-    create(:customer, firstname: 'Behalf of')
+    create(:customer, firstname: 'From')
   end
 
   describe 'request handling' do
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for customer by id' do
+    it 'does From auth - ticket create admin for customer by id' do
       params = {
         title:       'a new ticket #3',
         group:       'Users',
@@ -27,14 +27,14 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: customer.id)
+      authenticated_as(admin, from: customer.id)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:created)
       expect(json_response).to be_a_kind_of(Hash)
       expect(customer.id).to eq(json_response['created_by_id'])
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for customer by login (upcase)' do
+    it 'does From auth - ticket create admin for customer by login (upcase)' do
       params = {
         title:       'a new ticket #3',
         group:       'Users',
@@ -45,14 +45,14 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: customer.login.upcase)
+      authenticated_as(admin, from: customer.login.upcase)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:created)
       expect(json_response).to be_a_kind_of(Hash)
       expect(customer.id).to eq(json_response['created_by_id'])
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for customer by login' do
+    it 'does From auth - ticket create admin for customer by login' do
       ActivityStream.cleanup(1.year)
 
       params = {
@@ -65,7 +65,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: customer.login)
+      authenticated_as(admin, from: customer.login)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:created)
       json_response_ticket = json_response
@@ -108,7 +108,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
       expect(customer.id).to eq(ticket_created.created_by_id)
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for customer by email' do
+    it 'does From auth - ticket create admin for customer by email' do
       params = {
         title:       'a new ticket #3',
         group:       'Users',
@@ -119,14 +119,14 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: customer.email)
+      authenticated_as(admin, from: customer.email)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:created)
       expect(json_response).to be_a_kind_of(Hash)
       expect(customer.id).to eq(json_response['created_by_id'])
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for unknown' do
+    it 'does From auth - ticket create admin for unknown' do
       params = {
         title:       'a new ticket #3',
         group:       'Users',
@@ -137,7 +137,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: 99_449_494_949)
+      authenticated_as(admin, from: 99_449_494_949)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:forbidden)
       expect(@response.header).not_to be_key('Access-Control-Allow-Origin')
@@ -145,7 +145,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
       expect(json_response['error']).to eq("No such user '99449494949'")
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create customer for admin' do
+    it 'does From auth - ticket create customer for admin' do
       params = {
         title:       'a new ticket #3',
         group:       'Users',
@@ -156,15 +156,15 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(customer, on_behalf_of: admin.email)
+      authenticated_as(customer, from: admin.email)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:forbidden)
       expect(@response.header).not_to be_key('Access-Control-Allow-Origin')
       expect(json_response).to be_a_kind_of(Hash)
-      expect(json_response['error']).to eq("Current user has no permission to use 'X-On-Behalf-Of'!")
+      expect(json_response['error']).to eq("Current user has no permission to use 'From'/'X-On-Behalf-Of'!")
     end
 
-    it 'does X-On-Behalf-Of auth - ticket create admin for customer by email but no permitted action' do
+    it 'does From auth - ticket create admin for customer by email but no permitted action' do
       params = {
         title:       'a new ticket #3',
         group:       'secret1234',
@@ -175,7 +175,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
           body: 'some test 123',
         },
       }
-      authenticated_as(admin, on_behalf_of: customer.email)
+      authenticated_as(admin, from: customer.email)
       post '/api/v1/tickets', params: params, as: :json
       expect(response).to have_http_status(:unprocessable_entity)
       expect(@response.header).not_to be_key('Access-Control-Allow-Origin')
@@ -204,7 +204,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
             body: 'some test 123',
           },
         }
-        authenticated_as(admin, on_behalf_of: customer.email, token: token)
+        authenticated_as(admin, from: customer.email, token: token)
         post '/api/v1/tickets', params: params, as: :json
         expect(response).to have_http_status(:created)
         expect(json_response).to be_a_kind_of(Hash)
@@ -232,7 +232,7 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
             body: 'some test 123',
           },
         }
-        authenticated_as(admin, on_behalf_of: customer.email)
+        authenticated_as(admin, from: customer.email)
         post '/api/v1/tickets', params: params, as: :json
         expect(response).to have_http_status(:created)
         expect(customer.id).to eq(json_response['created_by_id'])
@@ -243,29 +243,29 @@ RSpec.describe 'Api Auth On Behalf Of', type: :request do
   end
 
   describe 'user lookup' do
-    it 'does X-On-Behalf-Of auth - user lookup by ID' do
-      authenticated_as(admin, on_behalf_of: customer.id)
+    it 'does From auth - user lookup by ID' do
+      authenticated_as(admin, from: customer.id)
       get '/api/v1/users/me', as: :json
       expect(json_response.fetch('id')).to be customer.id
     end
 
-    it 'does X-On-Behalf-Of auth - user lookup by login' do
-      authenticated_as(admin, on_behalf_of: customer.login)
+    it 'does From auth - user lookup by login' do
+      authenticated_as(admin, from: customer.login)
       get '/api/v1/users/me', as: :json
       expect(json_response.fetch('id')).to be customer.id
     end
 
-    it 'does X-On-Behalf-Of auth - user lookup by email' do
-      authenticated_as(admin, on_behalf_of: customer.email)
+    it 'does From auth - user lookup by email' do
+      authenticated_as(admin, from: customer.email)
       get '/api/v1/users/me', as: :json
       expect(json_response.fetch('id')).to be customer.id
     end
 
     # https://github.com/zammad/zammad/issues/2851
-    it 'does X-On-Behalf-Of auth - user lookup by email even if email starts with a digit' do
+    it 'does From auth - user lookup by email even if email starts with a digit' do
       customer.update! email: "#{agent.id}#{customer.email}"
 
-      authenticated_as(admin, on_behalf_of: customer.email)
+      authenticated_as(admin, from: customer.email)
       get '/api/v1/users/me', as: :json
       expect(json_response.fetch('id')).to be customer.id
     end
diff --git a/spec/support/request.rb b/spec/support/request.rb
index 452dd89cb..9783a9fcc 100644
--- a/spec/support/request.rb
+++ b/spec/support/request.rb
@@ -80,7 +80,7 @@ module ZammadSpecSupportRequest
     when :api_client
       # ensure that always the correct header value is set
       # otherwise previous header configurations will be re-used
-      add_headers('X-On-Behalf-Of' => options[:on_behalf_of])
+      add_headers('From' => options[:from])
 
       # if we want to authenticate by token
       credentials = if options[:token].present?