model: add EmailAutoconfig usecase interface and MailAutoconfigHost option

model/config.go

@@ -63,6 +63,11 @@ type Options struct {
 	// ...), when it needs to use complete URL, not only relative parts.
 	ExternalURL url.URL
 
+	// MailAutoconfigHost is the public FQDN that the email auto-configuration
+	// service should target with autoconfig./autodiscover. CNAMEs. When empty,
+	// it falls back to ExternalURL.Host.
+	MailAutoconfigHost string
+
 	// JWTSecretKey stores the private key to sign and verify JWT tokens.
 	JWTSecretKey []byte
 

model/email_autoconfig.go

@@ -0,0 +1,38 @@
+// This file is part of the happyDomain (R) project.
+// Copyright (c) 2020-2026 happyDomain
+// Authors: Pierre-Olivier Mercier, et al.
+//
+// This program is offered under a commercial and under the AGPL license.
+// For commercial licensing, contact us at <contact@happydomain.org>.
+//
+// For AGPL licensing:
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package happydns
+
+// EmailAutoconfigUsecase serves the public mail-client auto-configuration
+// endpoints (Mozilla Autoconfig + Microsoft Autodiscover).
+//
+// All methods take fully-qualified domain names. The usecase looks up the
+// owning Domain in storage, finds the latest Zone, and reads the
+// EmailAutoConfig service body to render the appropriate response.
+type EmailAutoconfigUsecase interface {
+	// MozillaConfig renders the Thunderbird-style XML for the given
+	// domain. emailAddress may be empty.
+	MozillaConfig(domainFQDN, emailAddress string) ([]byte, error)
+
+	// AutodiscoverConfig renders the Outlook-style XML for the given
+	// domain. emailAddress may be empty.
+	AutodiscoverConfig(domainFQDN, emailAddress string) ([]byte, error)
+}