diff --git a/database/migrations/2026_07_28_100000_seed_mailboxes_from_environment.php b/database/migrations/2026_07_28_100000_seed_mailboxes_from_environment.php
index 420efb0..6a0ba55 100644
--- a/database/migrations/2026_07_28_100000_seed_mailboxes_from_environment.php
+++ b/database/migrations/2026_07_28_100000_seed_mailboxes_from_environment.php
@@ -5,6 +5,7 @@ use App\Services\Mail\MailPurpose;
 use App\Services\Secrets\SecretCipher;
 use App\Support\Settings;
 use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\ConfigurationUrlParser;
 use Illuminate\Support\Facades\DB;
 
 /**
@@ -79,15 +80,58 @@ return new class extends Migration
         });
     }
 
+    /**
+     * host/port/username/password the way MailManager actually builds the
+     * SMTP transport from them — not necessarily what config('mail.mailers.
+     * smtp.host') and its three siblings hold.
+     *
+     * config/mail.php carries 'url' => env('MAIL_URL') on the smtp mailer:
+     * Laravel's OTHER supported way to configure SMTP, a single DSN instead
+     * of four separate variables. An install using it never sets MAIL_HOST/
+     * MAIL_USERNAME/MAIL_PASSWORD at all, so the plain config() calls this
+     * migration used to make read config/mail.php's own placeholder
+     * defaults (127.0.0.1, 2525, null, null) — indistinguishable from
+     * UNCONFIGURED_HOST/UNCONFIGURED_PORT below, even though the install
+     * sends mail successfully today. The substitution that would have shown
+     * the real values only happens inside Illuminate\Mail\MailManager::
+     * getConfig(), which is protected — not called here, reflected into, or
+     * re-implemented by hand (a second copy of ITS merge order is what would
+     * rot). Illuminate\Support\ConfigurationUrlParser is the public class
+     * getConfig() itself delegates to for exactly this, so calling it here
+     * directly is the same resolution, read from the one place it lives.
+     *
+     * Precedence — verified against the real MailManager::getConfig() via
+     * reflection, not guessed (see the task report): array_merge() puts
+     * parseConfiguration()'s result SECOND, and that result already has the
+     * URL's host/port/username/password merged in over top of the individual
+     * keys (Illuminate\Support\ConfigurationUrlParser::getPrimaryOptions()
+     * array_filters out only what the URL left null). So the URL wins for
+     * every field it actually supplies, and an unset MAIL_URL — isset() on a
+     * null config value is false, same as MailManager's own check — leaves
+     * this a no-op, returning the individual keys exactly as before.
+     */
+    private function resolveSmtpConfig(): array
+    {
+        $config = (array) config('mail.mailers.smtp', []);
+
+        if (! isset($config['url'])) {
+            return $config;
+        }
+
+        return array_merge($config, (new ConfigurationUrlParser)->parseConfiguration($config));
+    }
+
     private function seed(): void
     {
+        $smtp = $this->resolveSmtpConfig();
+
         // The server, once. Whatever .env already proved workable — but not
         // config/mail.php's own placeholder (see UNCONFIGURED_HOST above).
-        $configuredHost = (string) config('mail.mailers.smtp.host', '');
+        $configuredHost = (string) ($smtp['host'] ?? '');
         $host = $configuredHost === self::UNCONFIGURED_HOST ? '' : $configuredHost;
         Settings::set('mail.host', $host);
 
-        $configuredPort = (int) config('mail.mailers.smtp.port', 0);
+        $configuredPort = (int) ($smtp['port'] ?? 0);
         $port = $configuredPort === self::UNCONFIGURED_PORT ? 0 : $configuredPort;
         Settings::set('mail.port', $port);
 
@@ -101,7 +145,7 @@ return new class extends Migration
         // it is used: 465 means implicit TLS, everything else means STARTTLS.
         Settings::set('mail.encryption', $port === 465 ? 'ssl' : 'tls');
 
-        $configuredUser = (string) config('mail.mailers.smtp.username', '');
+        $configuredUser = (string) ($smtp['username'] ?? '');
 
         // Placeholder domain for the four boxes below comes from the SMTP
         // LOGIN's domain, not from mail.from.address — even though address
@@ -141,7 +185,7 @@ return new class extends Migration
         // moved: the app_secrets row is deliberately left in place below
         // rather than deleted, so this block only ever reads it.
         $storedPassword = DB::table('app_secrets')->where('key', 'mail.password')->value('value');
-        $envPassword = (string) config('mail.mailers.smtp.password', '');
+        $envPassword = (string) ($smtp['password'] ?? '');
 
         // A fresh install may not have generated SECRETS_KEY yet — encrypting
         // is what needs it, not migrating. Without this check, an install with
diff --git a/tests/Feature/Mail/MailboxSeedMigrationTest.php b/tests/Feature/Mail/MailboxSeedMigrationTest.php
index e43ced9..89575a7 100644
--- a/tests/Feature/Mail/MailboxSeedMigrationTest.php
+++ b/tests/Feature/Mail/MailboxSeedMigrationTest.php
@@ -68,6 +68,74 @@ it('still stores a deliberately configured host and port untouched', function ()
         ->and(Settings::get('mail.port'))->toBe(587);
 });
 
+it('resolves host, port, username and password from MAIL_URL when the individual SMTP keys are unset', function () {
+    // Codex R15#3, P1: an install may configure SMTP through Laravel's OTHER
+    // supported form, MAIL_URL (config/mail.php carries 'url' =>
+    // env('MAIL_URL')), instead of MAIL_HOST/MAIL_USERNAME/MAIL_PASSWORD.
+    // When it does, the individual keys sit at config/mail.php's own
+    // placeholder defaults below (127.0.0.1, 2525, null, null) because
+    // nothing ever set them — MailManager only substitutes the URL's
+    // components in at transport-build time, inside its own protected
+    // getConfig(). Read raw, as this migration used to, that is exactly
+    // UNCONFIGURED_HOST / UNCONFIGURED_PORT: it stored a blank host, port 0,
+    // and an unconfigured mailbox for an install that was sending mail
+    // successfully.
+    clearMailboxSeed();
+    config()->set('mail.mailers.smtp.host', '127.0.0.1');
+    config()->set('mail.mailers.smtp.port', 2525);
+    config()->set('mail.mailers.smtp.username', null);
+    config()->set('mail.mailers.smtp.password', null);
+    config()->set('mail.mailers.smtp.url', 'smtp://no-reply%40clupilot.com:s3cr%40t@smtp.clupilot.test:587');
+
+    loadMailboxSeedMigration()->up();
+
+    expect(Settings::get('mail.host'))->toBe('smtp.clupilot.test')
+        ->and(Settings::get('mail.port'))->toBe(587)
+        ->and(Settings::get('mail.encryption'))->toBe('tls');
+
+    $box = Mailbox::findByKey('no-reply');
+
+    // isConfigured() is exactly what MailboxResolver checks before handing a
+    // purpose to MailboxTransport — false here would mean every purpose
+    // mailer falls through to "unconfigured" and throws on send, the outage
+    // this finding describes.
+    expect($box->isConfigured())->toBeTrue()
+        ->and($box->smtpUsername())->toBe('no-reply@clupilot.com')
+        // Decoded from the URL's percent-encoding the same way MailManager
+        // decodes it (rawurldecode inside ConfigurationUrlParser), not left
+        // as the literal 's3cr%40t'.
+        ->and($box->password)->toBe('s3cr@t');
+});
+
+it("prefers MAIL_URL over the individual SMTP keys when both are set, matching MailManager's own precedence", function () {
+    // Verified against the real (protected) Illuminate\Mail\MailManager::
+    // getConfig() via reflection, not guessed: with both an 'url' and
+    // individually-set host/port/username/password present, the URL's
+    // components win for every field it supplies — Illuminate\Support\
+    // ConfigurationUrlParser::getPrimaryOptions() array_merges them in AFTER
+    // the individual keys, and array_filter there only drops what the URL
+    // left null. Decoy values stand in for the individual keys here
+    // specifically so a migration that read them instead of the URL would
+    // fail this test with THEIR value, not a blank one — the sibling test
+    // above already covers the blank/placeholder-default shape of the bug.
+    clearMailboxSeed();
+    config()->set('mail.mailers.smtp.host', 'decoy-host.invalid');
+    config()->set('mail.mailers.smtp.port', 9999);
+    config()->set('mail.mailers.smtp.username', 'decoy@invalid.test');
+    config()->set('mail.mailers.smtp.password', 'decoy-password');
+    config()->set('mail.mailers.smtp.url', 'smtp://no-reply%40clupilot.com:s3cr%40t@smtp.clupilot.test:587');
+
+    loadMailboxSeedMigration()->up();
+
+    expect(Settings::get('mail.host'))->toBe('smtp.clupilot.test')
+        ->and(Settings::get('mail.port'))->toBe(587);
+
+    $box = Mailbox::findByKey('no-reply');
+
+    expect($box->smtpUsername())->toBe('no-reply@clupilot.com')
+        ->and($box->password)->toBe('s3cr@t');
+});
+
 it('seeds address from mail.from.address and keeps the SMTP login as username when they differ', function () {
     // The installation this reproduces: MAIL_USERNAME is a relay login,
     // MAIL_FROM_ADDRESS is the address actually in force today. Before this