feat: add company links to Email Account and Communication (#49721)

Co-authored-by: barredterra <14891507+barredterra@users.noreply.github.com>

erpnext/setup/install.py

@@ -23,6 +23,7 @@ def after_install():
 	set_single_defaults()
 	create_print_setting_custom_fields()
 	create_marketgin_campagin_custom_fields()
+	create_custom_company_links()
 	add_all_roles_to("Administrator")
 	create_default_success_action()
 	create_incoterms()
@@ -139,6 +140,39 @@ def create_default_success_action():
 			doc.insert(ignore_permissions=True)
 
 
+def create_custom_company_links():
+	"""Add link fields to Company in Email Account and Communication.
+
+	These DocTypes are provided by the Frappe Framework but need to be associated
+	with a company in ERPNext to allow for multitenancy. I.e. one company should
+	not be able to access emails and communications from another company.
+	"""
+	create_custom_fields(
+		{
+			"Email Account": [
+				{
+					"label": _("Company"),
+					"fieldname": "company",
+					"fieldtype": "Link",
+					"options": "Company",
+					"insert_after": "email_id",
+				},
+			],
+			"Communication": [
+				{
+					"label": _("Company"),
+					"fieldname": "company",
+					"fieldtype": "Link",
+					"options": "Company",
+					"insert_after": "email_account",
+					"fetch_from": "email_account.company",
+					"read_only": 1,
+				},
+			],
+		},
+	)
+
+
 def add_company_to_session_defaults():
 	settings = frappe.get_single("Session Default Settings")
 	settings.append("session_defaults", {"ref_doctype": "Company"})