diff --git a/src/requests/zone.cr b/src/requests/zone.cr
index 2f9743a..0bff366 100644
--- a/src/requests/zone.cr
+++ b/src/requests/zone.cr
@@ -11,21 +11,22 @@ class DNSManager::Request
 		def handle(dnsmanagerd : DNSManager::Service, event : IPC::Event)
 			user = dnsmanagerd.get_logged_user event
 			raise NotLoggedException.new if user.nil?
-
-			# TODO: test for zone validity.
-			if errors = zone.get_errors?
-				return DNSManager::Response::InvalidZone.new errors
-			end
-
-			# In case there is no error, retrieve the zone in the DB.
-			#z = dnsmanagerd.storage.zones_by_domain.get? zone.domain
-			#if z
-			#else
-			#	dnsmanagerd.storage.zones << @zone
-			#end
-
-			Response::Success.new
+			dnsmanagerd.storage.add_or_update_zone user.uid, zone
 		end
 	end
 	DNSManager.requests << AddOrUpdateZone
+
+	IPC::JSON.message DeleteZone, 11 do
+		property domain : String
+
+		def initialize(@domain)
+		end
+
+		def handle(dnsmanagerd : DNSManager::Service, event : IPC::Event)
+			user = dnsmanagerd.get_logged_user event
+			raise NotLoggedException.new if user.nil?
+			dnsmanagerd.storage.delete_domain user.uid, @domain
+		end
+	end
+	DNSManager.requests << DeleteZone
 end
diff --git a/src/responses/user.cr b/src/responses/user.cr
new file mode 100644
index 0000000..c8ffab0
--- /dev/null
+++ b/src/responses/user.cr
@@ -0,0 +1,13 @@
+class DNSManager::Response
+	IPC::JSON.message UnknownUser, 50 do
+		def initialize
+		end
+	end
+	DNSManager.responses << UnknownUser
+
+	IPC::JSON.message NoOwnership, 51 do
+		def initialize
+		end
+	end
+	DNSManager.responses << NoOwnership
+end
diff --git a/src/responses/zone.cr b/src/responses/zone.cr
index b589002..927ca7a 100644
--- a/src/responses/zone.cr
+++ b/src/responses/zone.cr
@@ -2,10 +2,17 @@
 class DNSManager::Response
 	IPC::JSON.message InvalidZone, 10 do
 		# For now, Error is just an alias on String.
-		property errors : Array(DNSManager::Storage::Zone::Error)
+		property errors : Array(Storage::Zone::Error)
 		def initialize(@errors)
 		end
 	end
 	DNSManager.responses << InvalidZone
+
+	# Domain of a zone cannot change, for security reasons.
+	IPC::JSON.message DomainChanged, 11 do
+		def initialize
+		end
+	end
+	DNSManager.responses << DomainChanged
 end
 
diff --git a/src/storage.cr b/src/storage.cr
index 19c1621..8254fe1 100644
--- a/src/storage.cr
+++ b/src/storage.cr
@@ -44,21 +44,75 @@ class DNSManager::Storage
 		user_data_by_uid.update_or_create user_data.uid.to_s, user_data
 	end
 
-	def new_domain(user_id : Int32, zone : Zone)
-		user_data = user_data_by_uid.get? user_id.to_s
-		if user_data
-			# store the new zone
-			@zones << zone
+	def add_or_update_zone(user_id : Int32, zone : Zone)
 
-			# update user data only after ensuring this zone isn't already existing
-			user_data.domains << zone.domain
-			update_user_data user_data
-		else
-			Baguette::Log.error "trying to add zone #{zone.domain} to unknown user #{user_id}"
+		# Test zone validity.
+		if errors = zone.get_errors?
+			Baguette::Log.warning "zone #{zone.domain} update with errors: #{errors}"
+			return DNSManager::Response::InvalidZone.new errors
 		end
+
+		# User must exist.
+		user_data = user_data_by_uid.get? user_id.to_s
+		unless user_data
+			Baguette::Log.warning "unknown user #{user_id} tries to add -or update- zone #{zone.domain}"
+			return Response::UnknownUser.new
+		end
+
+		# Does the zone already exist?
+		if z = zones_by_domain.get? zone.domain
+			# User must own the zone.
+			unless user_data.domains.includes? zone.domain
+				Baguette::Log.warning "user #{user_id} doesn't own domain #{zone.domain}"
+				return Response::NoOwnership.new
+			end
+
+			# Domain cannot change (for security reasons).
+			unless z.domain == zone.domain
+				Baguette::Log.warning "user #{user_id} tries to change domain #{z.domain} by #{zone.domain}"
+				return Response::DomainChanged.new
+			end
+		else
+			# Add the domain to the user's domain.
+			user_data.domains << zone.domain
+
+			# Actually write data on-disk.
+			update_user_data user_data
+		end
+
+		# Add -or replace- the zone.
+		zones_by_domain.update_or_create zone.domain, zone
+
+		Response::Success.new
 	rescue e
-		Baguette::Log.error "trying to add zone #{zone.domain} #{e}"
+		Baguette::Log.error "trying to add -or update- zone #{zone.domain}: #{e}"
+		Response::Error.new "error while updating the domain #{zone.domain}"
 	end
+
+	def delete_domain(user_id : Int32, domain : String)
+		# User must exist.
+		user_data = user_data_by_uid.get? user_id.to_s
+		unless user_data
+			Baguette::Log.warning "unknown user #{user_id} tries to delete domain #{domain}"
+			return Response::UnknownUser.new
+		end
+
+		# User must own the domain.
+		unless user_data.domains.includes? domain
+			Baguette::Log.warning "user #{user_id} tries to delete domain #{domain} doesn't own it"
+			return Response::NoOwnership.new
+		end
+
+		# TODO: remove this domain from the list of user's domains.
+		# TODO: remove the related zone.
+		#unless errors = Storage::Zone.is_domain_valid? domain
+		#	return Response::InvalidZone.new errors
+		#end
+	rescue e
+		Baguette::Log.error "trying to delete a domain #{domain}: #{e}"
+		Response::Error.new "error while deleting the domain #{domain}"
+	end
+
 end
 
 require "./storage/*"