diff --git a/src/BusProNet/Model/Communication.php b/src/BusProNet/Model/Communication.php
index 2a3c17d..474feca 100644
--- a/src/BusProNet/Model/Communication.php
+++ b/src/BusProNet/Model/Communication.php
@@ -39,7 +39,9 @@ class Communication
 
     public function setEmail(?string $email): static
     {
-        $this->email = $email;
+        // BusPro compares addresses case-insensitively; normalize on the way in so the DTO
+        // carries the same shape the entities store.
+        $this->email = null === $email ? null : mb_strtolower(trim($email));
 
         return $this;
     }
diff --git a/src/Entity/Contact.php b/src/Entity/Contact.php
index 8e56752..9f096cc 100644
--- a/src/Entity/Contact.php
+++ b/src/Entity/Contact.php
@@ -75,7 +75,7 @@ class Contact
 
     public function setEmail(string $email): static
     {
-        $this->email = $email;
+        $this->email = mb_strtolower(trim($email));
 
         return $this;
     }
diff --git a/src/Entity/Embeddable/Communication.php b/src/Entity/Embeddable/Communication.php
index 2513c81..a023d71 100644
--- a/src/Entity/Embeddable/Communication.php
+++ b/src/Entity/Embeddable/Communication.php
@@ -108,7 +108,7 @@ class Communication
 
     public function setEmail(?string $email): static
     {
-        $this->email = $email;
+        $this->email = null === $email ? null : mb_strtolower(trim($email));
 
         return $this;
     }
diff --git a/src/Security/BpnAuthenticator.php b/src/Security/BpnAuthenticator.php
index b8b06db..808760d 100644
--- a/src/Security/BpnAuthenticator.php
+++ b/src/Security/BpnAuthenticator.php
@@ -43,7 +43,7 @@ class BpnAuthenticator extends AbstractLoginFormAuthenticator implements Authent
 
     public function authenticate(Request $request): Passport
     {
-        $email = trim($request->request->getString('_username'));
+        $email = mb_strtolower(trim($request->request->getString('_username')));
         $passwordPlain = trim($request->request->getString('_password'));
 
         // Very lame hashing applied here as required by BPN
diff --git a/tests/BusProNet/UserDataHandlerTest.php b/tests/BusProNet/UserDataHandlerTest.php
index f07f4f7..eec0db4 100644
--- a/tests/BusProNet/UserDataHandlerTest.php
+++ b/tests/BusProNet/UserDataHandlerTest.php
@@ -200,6 +200,37 @@ class UserDataHandlerTest extends TestCase
         $this->assertSame(['team' => ['selected' => true]], $teamer->getCrmSelections());
     }
 
+    /**
+     * BusPro compares addresses case-insensitively and MyE&P lowercases them on login, so a
+     * mixed-case address coming back from the API must land lowercased on both the user and
+     * the teamer - otherwise the login identity and the mailing address drift apart.
+     */
+    public function testUpdateLocalUserNormalizesTheAddressBusProReports(): void
+    {
+        $user = (new User())
+            ->setFirstName('Old')
+            ->setLastName('Name')
+            ->setEmail('old@example.com')
+            ->setBusProAddressId(1)
+            ->setBusProPersonId(2)
+        ;
+
+        $teamer = (new Teamer())
+            ->setCommunication((new Communication())->setEmail('old@example.com'))
+        ;
+        $user->setTeamer($teamer);
+
+        $profileResponse = $this->createProfileResponse()
+            ->setCommunication((new BusProCommunication())->setEmail('New.User@Example.COM'))
+        ;
+
+        $handler = new UserDataHandler($this->entityManager, $this->logger);
+        $handler->updateLocalUser($user, $profileResponse, true, [], ['ROLE_TEAMER'], []);
+
+        $this->assertSame('new.user@example.com', $user->getEmail());
+        $this->assertSame('new.user@example.com', $teamer->getCommunication()?->getEmail());
+    }
+
     /**
      * @dataProvider pendingRolesProvider
      */
diff --git a/tests/Entity/ContactTest.php b/tests/Entity/ContactTest.php
new file mode 100644
index 0000000..0808817
--- /dev/null
+++ b/tests/Entity/ContactTest.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Entity;
+
+use App\Entity\Contact;
+use PHPUnit\Framework\TestCase;
+
+class ContactTest extends TestCase
+{
+    /**
+     * Office contacts are normalized the same way User::setEmail() normalizes, so that every
+     * stored address has one shape regardless of which form wrote it.
+     */
+    public function testSetEmailNormalizesCaseAndSurroundingWhitespace(): void
+    {
+        $contact = (new Contact())->setEmail('  Buero@EP-Reisen.DE ');
+
+        $this->assertSame('buero@ep-reisen.de', $contact->getEmail());
+    }
+}
diff --git a/tests/Entity/Embeddable/CommunicationTest.php b/tests/Entity/Embeddable/CommunicationTest.php
new file mode 100644
index 0000000..9623d93
--- /dev/null
+++ b/tests/Entity/Embeddable/CommunicationTest.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Entity\Embeddable;
+
+use App\Entity\Embeddable\Communication;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Pins the lowercasing of the teamer's contact address. This is the address the profile form
+ * writes and the one toPayload() pushes back to BusPro, so a mixed-case value entered here
+ * would otherwise diverge from the login identity stored in User::email.
+ */
+class CommunicationTest extends TestCase
+{
+    public function testSetEmailNormalizesCaseAndSurroundingWhitespace(): void
+    {
+        $communication = (new Communication())->setEmail('  Max.Mustermann@EP-Reisen.DE ');
+
+        $this->assertSame('max.mustermann@ep-reisen.de', $communication->getEmail());
+    }
+
+    public function testSetEmailKeepsNull(): void
+    {
+        $communication = (new Communication())->setEmail(null);
+
+        $this->assertNull($communication->getEmail());
+    }
+
+    /**
+     * The outbound BusPro payload must carry the normalized form, not the raw input.
+     */
+    public function testPayloadCarriesTheNormalizedAddress(): void
+    {
+        $communication = (new Communication())
+            ->setEmail('Max.Mustermann@EP-Reisen.DE')
+            ->setMobile('0170 1234567')
+        ;
+
+        $this->assertSame('max.mustermann@ep-reisen.de', $communication->toPayload()['email']);
+    }
+}