diff --git a/app/V1Module/presenters/RegistrationPresenter.php b/app/V1Module/presenters/RegistrationPresenter.php
index eebe4a408..2fb44a964 100644
--- a/app/V1Module/presenters/RegistrationPresenter.php
+++ b/app/V1Module/presenters/RegistrationPresenter.php
@@ -3,6 +3,7 @@
 namespace App\V1Module\Presenters;
 
 use App\Helpers\MetaFormats\Attributes\Post;
+use App\Helpers\MetaFormats\Validators\VBool;
 use App\Helpers\MetaFormats\Validators\VEmail;
 use App\Helpers\MetaFormats\Validators\VMixed;
 use App\Helpers\MetaFormats\Validators\VString;
@@ -162,6 +163,12 @@ public function checkCreateAccount()
     #[Post("instanceId", new VString(1), "Identifier of the instance to register in")]
     #[Post("titlesBeforeName", new VString(1), "Titles which is placed before user name", required: false)]
     #[Post("titlesAfterName", new VString(1), "Titles which is placed after user name", required: false)]
+    #[Post(
+        "ignoreNameCollision",
+        new VBool(),
+        "If a use with the same name exists, this needs to be set to true.",
+        required: false
+    )]
     public function actionCreateAccount()
     {
         $req = $this->getRequest();
@@ -169,15 +176,23 @@ public function actionCreateAccount()
         // check if the email is free
         $email = trim($req->getPost("email"));
         // username is name of column which holds login identifier represented by email
-        if ($this->logins->getByUsername($email) !== null) {
-            throw new BadRequestException("This email address is already taken.");
+        if ($this->logins->getByUsername($email) !== null || $this->users->getByEmail($email) !== null) {
+            throw new BadRequestException(
+                "This email address is already taken.",
+                FrontendErrorMappings::E400_110__USER_EMAIL_ALREADY_EXISTS
+            );
         }
 
         $instanceId = $req->getPost("instanceId");
         $instance = $this->getInstance($instanceId);
 
-        $titlesBeforeName = $req->getPost("titlesBeforeName") === null ? "" : $req->getPost("titlesBeforeName");
-        $titlesAfterName = $req->getPost("titlesAfterName") === null ? "" : $req->getPost("titlesAfterName");
+        $titlesBeforeName = trim($req->getPost("titlesBeforeName") ?? "");
+        $titlesAfterName = trim($req->getPost("titlesAfterName") ?? "");
+        $firstName = trim($req->getPost("firstName") ?? "");
+        $lastName = trim($req->getPost("lastName") ?? "");
+        if (!$firstName || !$lastName) {
+            throw new BadRequestException("The user's full name must be filled in.");
+        }
 
         // check given passwords
         $password = $req->getPost("password");
@@ -189,10 +204,23 @@ public function actionCreateAccount()
             );
         }
 
+        // Check for name collisions, unless the request explicitly says to ignore them.
+        if (!$req->getPost("ignoreNameCollision")) {
+            $sameName = $this->users->findByName($instance, $firstName, $lastName);
+            if ($sameName) {
+                // let's report the colliding users
+                $this->sendSuccessResponse([
+                    "user" => null,
+                    "usersWithSameName" => $this->userViewFactory->getUsers($sameName),
+                ]);
+                return;
+            }
+        }
+
         $user = new User(
             $email,
-            $req->getPost("firstName"),
-            $req->getPost("lastName"),
+            $firstName,
+            $lastName,
             $titlesBeforeName,
             $titlesAfterName,
             Roles::STUDENT_ROLE,
@@ -272,31 +300,49 @@ public function actionCreateInvitation()
         // check if the email is free
         $email = trim($format->email);
         // username is name of column which holds login identifier represented by email
-        if ($this->logins->getByUsername($email) !== null) {
-            throw new BadRequestException("This email address is already taken.");
+        if ($this->logins->getByUsername($email) !== null || $this->users->getByEmail($email) !== null) {
+            throw new BadRequestException(
+                "This email address is already taken.",
+                FrontendErrorMappings::E400_110__USER_EMAIL_ALREADY_EXISTS
+            );
         }
 
         $groupsIds = $format->groups ?? [];
         foreach ($groupsIds as $id) {
             $group = $this->groups->get($id);
             if (!$group || $group->isOrganizational() || !$this->groupAcl->canInviteStudents($group)) {
-                throw new BadRequestException("Current user cannot invite people in group '$id'");
+                throw new ForbiddenRequestException("Current user cannot invite people in group '$id'");
             }
         }
 
         // gather data
         $instanceId = $format->instanceId;
-        $instance = $this->getInstance($instanceId);
-        $titlesBeforeName = $format->titlesBeforeName === null ? "" : $format->titlesBeforeName;
-        $titlesAfterName = $format->titlesAfterName === null ? "" : $format->titlesAfterName;
+        $instance = $this->getInstance($instanceId); // we don't need it, just to check it exists
+        $titlesBeforeName = $format->titlesBeforeName === null ? "" : trim($format->titlesBeforeName);
+        $titlesAfterName = $format->titlesAfterName === null ? "" : trim($format->titlesAfterName);
+        $firstName = trim($format->firstName);
+        $lastName = trim($format->lastName);
+        if (!$firstName || !$lastName) {
+            throw new BadRequestException("The user's full name must be filled in.");
+        }
+
+        // Check for name collisions, unless the request explicitly says to ignore them.
+        if (!$format->ignoreNameCollision) {
+            $sameName = $this->users->findByName($instance, $firstName, $lastName);
+            if ($sameName) {
+                // let's report the colliding users
+                $this->sendSuccessResponse($this->userViewFactory->getUsers($sameName));
+                return;
+            }
+        }
 
         // create the token and send it via email
         try {
             $this->invitationHelper->invite(
                 $instanceId,
                 $email,
-                $format->firstName,
-                $format->lastName,
+                $firstName,
+                $lastName,
                 $titlesBeforeName,
                 $titlesAfterName,
                 $groupsIds,
diff --git a/app/exceptions/FrontendErrorMappings.php b/app/exceptions/FrontendErrorMappings.php
index 8e3449f1b..b5cd246dd 100644
--- a/app/exceptions/FrontendErrorMappings.php
+++ b/app/exceptions/FrontendErrorMappings.php
@@ -34,6 +34,8 @@ class FrontendErrorMappings
     public const E400_104__EXTERNAL_AUTH_FAILED_USER_NOT_FOUND = "400-104";
     /** External authentication failed - unable to register new user because no role was provided. */
     public const E400_105__EXTERNAL_AUTH_FAILED_MISSING_ROLE = "400-105";
+    /** User email already exists, new user cannot be created/invited/registered/.... */
+    public const E400_110__USER_EMAIL_ALREADY_EXISTS = "400-110";
 
     /** General job config error */
     public const E400_200__JOB_CONFIG = "400-200";
diff --git a/app/helpers/MetaFormats/FormatDefinitions/UserFormat.php b/app/helpers/MetaFormats/FormatDefinitions/UserFormat.php
index d400a9097..a77d61f58 100644
--- a/app/helpers/MetaFormats/FormatDefinitions/UserFormat.php
+++ b/app/helpers/MetaFormats/FormatDefinitions/UserFormat.php
@@ -4,10 +4,9 @@
 
 use App\Helpers\MetaFormats\Attributes\Format;
 use App\Helpers\MetaFormats\MetaFormat;
-use App\Helpers\MetaFormats\Attributes\FormatParameterAttribute;
 use App\Helpers\MetaFormats\Attributes\FPost;
-use App\Helpers\MetaFormats\Type;
 use App\Helpers\MetaFormats\Validators\VArray;
+use App\Helpers\MetaFormats\Validators\VBool;
 use App\Helpers\MetaFormats\Validators\VEmail;
 use App\Helpers\MetaFormats\Validators\VString;
 use App\Helpers\MetaFormats\Validators\VUuid;
@@ -41,4 +40,7 @@ class UserFormat extends MetaFormat
 
     #[FPost(new VString(2, 2), "Language used in the invitation email (en by default).", required: false)]
     public ?string $locale;
+
+    #[FPost(new VBool(), "If a use with the same name exists, this needs to be set to true.", required: false)]
+    public ?bool $ignoreNameCollision;
 }
diff --git a/app/model/repository/Users.php b/app/model/repository/Users.php
index 5ddb27e36..ec483b70d 100644
--- a/app/model/repository/Users.php
+++ b/app/model/repository/Users.php
@@ -5,6 +5,7 @@
 use App\Helpers\Pagination;
 use App\Model\Helpers\PaginationDbHelper;
 use App\Model\Entity\User;
+use App\Model\Entity\Instance;
 use DateTime;
 use Doctrine\ORM\EntityManagerInterface;
 
@@ -55,7 +56,7 @@ public function getPaginated(Pagination $pagination, &$totalCount): array
                 'email' => ['u.email'],
                 'createdAt' => ['u.createdAt'],
             ],
-            ['firstName', 'lastName'] // search column names
+            ['firstName', 'lastName', 'email'] // search column names
         );
         $paginationDbHelper->apply($qb, $pagination);
 
@@ -75,7 +76,7 @@ public function getPaginated(Pagination $pagination, &$totalCount): array
 
 
     /**
-     * Search users first names and surnames based on given string.
+     * Search users first names and surnames based on given (sub)string.
      * @param string|null $search
      * @return User[]
      */
@@ -93,6 +94,21 @@ public function findByRoles(string ...$roles): array
         return $this->findBy(["role" => $roles]);
     }
 
+    /**
+     * Find users by exact match of the whole name.
+     * @param Instance $instance
+     * @param string $firstName
+     * @param string $lastName
+     * @return User[]
+     */
+    public function findByName(Instance $instance, string $firstName, string $lastName): array
+    {
+        $users = $this->findBy(["firstName" => $firstName, "lastName" => $lastName]);
+        return array_filter($users, function (User $user) use ($instance) {
+            return $user->belongsTo($instance);
+        });
+    }
+
     /**
      * Find all users who have not authenticated to the system for some time.
      * @param DateTime|null $before Only users with last activity before given date
diff --git a/tests/Presenters/RegistrationPresenter.phpt b/tests/Presenters/RegistrationPresenter.phpt
index 2d93c9526..469f08ac3 100644
--- a/tests/Presenters/RegistrationPresenter.phpt
+++ b/tests/Presenters/RegistrationPresenter.phpt
@@ -79,8 +79,8 @@ class TestRegistrationPresenter extends Tester\TestCase
         $this->presenter = PresenterTestHelper::createPresenter($this->container, RegistrationPresenter::class);
         $this->presenter->registrationConfig = new RegistrationConfig(
             [
-            'enabled' => true,
-            'implicitGroupsIds' => []
+                'enabled' => true,
+                'implicitGroupsIds' => []
             ]
         );
 
@@ -118,14 +118,14 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $password,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
         $response = $this->presenter->run($request);
@@ -170,20 +170,20 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $password,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
         $this->presenter->registrationConfig = new RegistrationConfig(
             [
-            'enabled' => true,
-            'implicitGroupsIds' => [$groupId]
+                'enabled' => true,
+                'implicitGroupsIds' => [$groupId]
             ]
         );
         $response = $this->presenter->run($request);
@@ -226,19 +226,19 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $password,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
         $this->presenter->registrationConfig = new RegistrationConfig(
             [
-            'enabled' => false,
+                'enabled' => false,
             ]
         );
 
@@ -265,14 +265,14 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $password,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
 
@@ -302,14 +302,14 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $passwordConfirm,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $passwordConfirm,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
 
@@ -336,14 +336,14 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'createAccount'],
             [
-            'email' => $email,
-            'firstName' => $firstName,
-            'lastName' => $lastName,
-            'password' => $password,
-            'passwordConfirm' => $password,
-            'instanceId' => $instanceId,
-            'titlesBeforeName' => $titlesBeforeName,
-            'titlesAfterName' => $titlesAfterName
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
             ]
         );
 
@@ -356,6 +356,93 @@ class TestRegistrationPresenter extends Tester\TestCase
         );
     }
 
+    public function testCreateAccountSameName()
+    {
+        $student = $this->presenter->users->getByEmail(PresenterTestHelper::STUDENT_GROUP_MEMBER_LOGIN);
+        Assert::notNull($student);
+
+        $email = "email@email.email";
+        $firstName = $student->getFirstName();
+        $lastName = $student->getLastName();
+        $password = "password";
+        $instances = $this->instances->findAll();
+        $instanceId = array_pop($instances)->getId();
+        $titlesBeforeName = "titlesBeforeName";
+        $titlesAfterName = "titlesAfterName";
+
+        $payload = PresenterTestHelper::performPresenterRequest(
+            $this->presenter,
+            $this->presenterPath,
+            'POST',
+            ['action' => 'createAccount'],
+            [
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName
+            ]
+        );
+
+        Assert::equal(null, $payload["user"]);
+        Assert::count(1, $payload["usersWithSameName"]);
+        $user = current($payload["usersWithSameName"]);
+        Assert::equal($student->getId(), $user["id"]);
+    }
+
+    public function testCreateAccountSameNameEnabled()
+    {
+        $student = $this->presenter->users->getByEmail(PresenterTestHelper::STUDENT_GROUP_MEMBER_LOGIN);
+        Assert::notNull($student);
+
+        $email = "email@email.email";
+        $firstName = $student->getFirstName();
+        $lastName = $student->getLastName();
+        $password = "password";
+        $instances = $this->instances->findAll();
+        $instanceId = array_pop($instances)->getId();
+        $titlesBeforeName = "titlesBeforeName";
+        $titlesAfterName = "titlesAfterName";
+
+        $request = new Nette\Application\Request(
+            $this->presenterPath,
+            'POST',
+            ['action' => 'createAccount'],
+            [
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'password' => $password,
+                'passwordConfirm' => $password,
+                'instanceId' => $instanceId,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName,
+                'ignoreNameCollision' => true,
+            ]
+        );
+        $response = $this->presenter->run($request);
+        Assert::type(Nette\Application\Responses\JsonResponse::class, $response);
+
+        $result = $response->getPayload();
+        Assert::equal(201, $result['code']);
+        Assert::equal(2, count($result['payload']));
+        Assert::true(array_key_exists("accessToken", $result["payload"]));
+        Assert::true(array_key_exists("user", $result["payload"]));
+
+        // check created user
+        $user = $result["payload"]["user"];
+        Assert::equal("$titlesBeforeName $firstName $lastName $titlesAfterName", $user["fullName"]);
+        Assert::equal($email, $user["privateData"]["email"]);
+
+        // check created login
+        $login = $this->logins->findByUserId($user["id"]);
+        Assert::equal($user["id"], $login->getUser()->getId());
+        Assert::true($login->passwordsMatchOrEmpty($password, $this->presenter->passwordsService));
+    }
+
     public function testValidateRegistrationData()
     {
         $request = new Nette\Application\Request(
@@ -363,8 +450,8 @@ class TestRegistrationPresenter extends Tester\TestCase
             'POST',
             ['action' => 'validateRegistrationData'],
             [
-            'email' => "totallyFreeEmail@EmailFreeTotally.freeEmailTotally",
-            'password' => "totallySecurePasswordWhichIsNot123456"
+                'email' => "totallyFreeEmail@EmailFreeTotally.freeEmailTotally",
+                'password' => "totallySecurePasswordWhichIsNot123456"
             ]
         );
         $response = $this->presenter->run($request);
@@ -511,10 +598,101 @@ class TestRegistrationPresenter extends Tester\TestCase
                     ]
                 );
             },
-            BadRequestException::class
+            ForbiddenRequestException::class
         );
     }
 
+    public function testCreateInvitationWithSameName()
+    {
+        $student = $this->presenter->users->getByEmail(PresenterTestHelper::STUDENT_GROUP_MEMBER_LOGIN);
+        Assert::notNull($student);
+
+        $email = "newguy@recodex.com";
+        $firstName = $student->getFirstName();
+        $lastName = $student->getLastName();
+        $instances = $this->instances->findAll();
+        $instanceId = array_pop($instances)->getId();
+        $titlesBeforeName = "titlesBeforeName";
+        $titlesAfterName = "titlesAfterName";
+
+        $groups = [];
+        foreach ($this->presenter->groups->findAll() as $group) {
+            if (!$group->isArchived() && !$group->isOrganizational()) {
+                $groups[] = $group->getId();
+            }
+        }
+        Assert::truthy($groups);
+
+        PresenterTestHelper::loginDefaultAdmin($this->container);
+        $payload = PresenterTestHelper::performPresenterRequest(
+            $this->presenter,
+            $this->presenterPath,
+            'POST',
+            ['action' => 'createInvitation'],
+            [
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName,
+                'instanceId' => $instanceId,
+                'groups' => $groups,
+                'locale' => 'en',
+            ]
+        );
+
+        Assert::count(1, $payload);
+        $user = current($payload);
+        Assert::equal($student->getId(), $user["id"]);
+    }
+
+    public function testCreateInvitationWithSameNameEnabled()
+    {
+        $student = $this->presenter->users->getByEmail(PresenterTestHelper::STUDENT_GROUP_MEMBER_LOGIN);
+        Assert::notNull($student);
+
+        $email = "newguy@recodex.com";
+        $firstName = $student->getFirstName();
+        $lastName = $student->getLastName();
+        $instances = $this->instances->findAll();
+        $instanceId = array_pop($instances)->getId();
+        $titlesBeforeName = "titlesBeforeName";
+        $titlesAfterName = "titlesAfterName";
+
+        $groups = [];
+        foreach ($this->presenter->groups->findAll() as $group) {
+            if (!$group->isArchived() && !$group->isOrganizational()) {
+                $groups[] = $group->getId();
+            }
+        }
+        Assert::truthy($groups);
+
+        $this->emailHelperMock->shouldReceive("send")
+            ->with("noreply@recodex", [$email], "en", 'User Admin Admin has invited you in ReCodEx!', Mockery::any())
+            ->once()->andReturn(true);
+
+        PresenterTestHelper::loginDefaultAdmin($this->container);
+        $payload = PresenterTestHelper::performPresenterRequest(
+            $this->presenter,
+            $this->presenterPath,
+            'POST',
+            ['action' => 'createInvitation'],
+            [
+                'email' => $email,
+                'firstName' => $firstName,
+                'lastName' => $lastName,
+                'titlesBeforeName' => $titlesBeforeName,
+                'titlesAfterName' => $titlesAfterName,
+                'instanceId' => $instanceId,
+                'groups' => $groups,
+                'locale' => 'en',
+                'ignoreNameCollision' => true,
+            ]
+        );
+
+        Assert::equal("OK", $payload);
+    }
+
     public function testAcceptInvitation()
     {
         $email = "newguy@recodex.com";