diff --git a/appinfo/info.xml b/appinfo/info.xml
index c51cb1cd..c1295f66 100755
--- a/appinfo/info.xml
+++ b/appinfo/info.xml
@@ -36,6 +36,7 @@ Guests users can only access files shared to them and cannot create any files ou
 	<repair-steps>
 		<post-migration>
 			<step>OCA\Guests\Migration\OwncloudGuestsMigration</step>
+			<step>OCA\Guests\Repair\ResetEmails</step>
 		</post-migration>
 	</repair-steps>
 	<commands>
diff --git a/lib/Repair/ResetEmails.php b/lib/Repair/ResetEmails.php
new file mode 100644
index 00000000..9568b4da
--- /dev/null
+++ b/lib/Repair/ResetEmails.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2025 Robin Appelman <robin@icewind.nl>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\Guests\Repair;
+
+use OCA\Guests\GuestManager;
+use OCP\IConfig;
+use OCP\IUserManager;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+
+class ResetEmails implements IRepairStep {
+	public function __construct(
+		private readonly GuestManager $guestManager,
+		private readonly IUserManager $userManager,
+		private readonly IConfig $config,
+	) {
+	}
+
+	public function getName(): string {
+		return 'Reset the email of all guest accounts';
+	}
+
+	public function run(IOutput $output) {
+		foreach ($this->guestManager->listGuests() as $guestId) {
+			$guest = $this->userManager->get($guestId);
+			if (strtolower($guest->getSystemEMailAddress()) !== strtolower($guestId)) {
+				$this->config->setUserValue($guestId, 'guests', 'old_email', $guest->getSystemEMailAddress());
+				$guest->setSystemEMailAddress(strtolower($guestId));
+			}
+		}
+	}
+}