diff --git a/flexiapi/.env.example b/flexiapi/.env.example
index 4a32a49..626f1d9 100644
--- a/flexiapi/.env.example
+++ b/flexiapi/.env.example
@@ -20,6 +20,7 @@ ACCOUNT_TRANSPORT_PROTOCOL_TEXT="TLS (recommended), TCP or UDP" # Simple text, t
 ACCOUNT_REALM=null # Default realm for the accounts, fallback to the domain if not set, enforce null by default
 
 # Account creation
+ACCOUNT_EMAIL_UNIQUE=false # Emails are unique between all the accounts
 ACCOUNT_CONSUME_EXTERNAL_ACCOUNT_ON_CREATE=false
 ACCOUNT_BLACKLISTED_USERNAMES=
 
diff --git a/flexiapi/app/Http/Controllers/Account/AuthenticateController.php b/flexiapi/app/Http/Controllers/Account/AuthenticateController.php
index 5ddb55c..96988bf 100644
--- a/flexiapi/app/Http/Controllers/Account/AuthenticateController.php
+++ b/flexiapi/app/Http/Controllers/Account/AuthenticateController.php
@@ -52,7 +52,7 @@ class AuthenticateController extends Controller
         ]);
 
         $account = Account::where('username', $request->get('username'))
-                          ->first();
+            ->first();
 
         // Try alias
         if (!$account) {
@@ -104,9 +104,13 @@ class AuthenticateController extends Controller
         /**
          * Because several accounts can have the same email
          */
-        $account = Account::where('email', $request->get('email'))
-                          ->where('username', $request->get('username'))
-                          ->first();
+        $account = Account::where('username', $request->get('username'));
+
+        if (config('app.account_email_unique') == false) {
+            $account = $account->where('email', $request->get('email'));
+        }
+
+        $account = $account->first();
 
         // Try alias
         if (!$account) {
@@ -148,7 +152,7 @@ class AuthenticateController extends Controller
     public function validateEmail(Request $request, string $code)
     {
         $request->merge(['code' => $code]);
-        $request->validate(['code' => 'required|size:'.self::$emailCodeSize]);
+        $request->validate(['code' => 'required|size:' . self::$emailCodeSize]);
 
         $account = Account::where('confirmation_key', $code)->first();
 
@@ -188,7 +192,7 @@ class AuthenticateController extends Controller
         ]);
 
         $account = Account::where('username', $request->get('phone'))
-                          ->first();
+            ->first();
 
         // Try alias
         if (!$account) {
@@ -209,7 +213,7 @@ class AuthenticateController extends Controller
         $account->save();
 
         $ovhSMS = new OvhSMS;
-        $ovhSMS->send($request->get('phone'), 'Your '.config('app.name').' validation code is '.$account->confirmation_key);
+        $ovhSMS->send($request->get('phone'), 'Your ' . config('app.name') . ' validation code is ' . $account->confirmation_key);
 
         // Ask the user to set a password
         if (!$account->activated) {
@@ -229,7 +233,7 @@ class AuthenticateController extends Controller
         ]);
 
         $account = Account::where('id', $request->get('account_id'))
-                          ->firstOrFail();
+            ->firstOrFail();
 
         if ($account->confirmation_key != $request->get('code')) {
             return redirect()->back()->withErrors([
diff --git a/flexiapi/app/Http/Controllers/Account/EmailController.php b/flexiapi/app/Http/Controllers/Account/EmailController.php
index f555f15..f650870 100644
--- a/flexiapi/app/Http/Controllers/Account/EmailController.php
+++ b/flexiapi/app/Http/Controllers/Account/EmailController.php
@@ -42,10 +42,14 @@ class EmailController extends Controller
             $request->user()->email
                 ? [
                     'email_current' => ['required', Rule::in([$request->user()->email])],
-                    'email' => 'required|different:email_current|confirmed|email',
+                    'email' => config('app.account_email_unique')
+                        ? 'required|different:email_current|confirmed|email|unique:accounts,email'
+                        : 'required|different:email_current|confirmed|email',
                 ]
                 : [
-                    'email' => 'required|confirmed|email',
+                    'email' => config('app.account_email_unique')
+                        ? 'required|email|confirmed|unique:accounts,email'
+                        : 'required|confirmed|email',
                 ]
         );
 
diff --git a/flexiapi/app/Http/Controllers/Account/RegisterController.php b/flexiapi/app/Http/Controllers/Account/RegisterController.php
index 341e3bd..fa99b6b 100644
--- a/flexiapi/app/Http/Controllers/Account/RegisterController.php
+++ b/flexiapi/app/Http/Controllers/Account/RegisterController.php
@@ -84,7 +84,9 @@ class RegisterController extends Controller
                 new BlacklistedUsername
             ],
             'g-recaptcha-response'  => 'required|captcha',
-            'email' => 'required|email|confirmed'
+            'email' => config('app.account_email_unique')
+                ? 'required|email|confirmed|unique:accounts,email'
+                : 'required|email|confirmed',
         ]);
 
         $account = new Account;
@@ -100,8 +102,7 @@ class RegisterController extends Controller
         $account->confirmation_key = Str::random($this->emailCodeSize);
         $account->save();
 
-        if (!empty(config('app.newsletter_registration_address'))
-         && $request->has('newsletter')) {
+        if (!empty(config('app.newsletter_registration_address')) && $request->has('newsletter')) {
             Mail::to(config('app.newsletter_registration_address'))->send(new NewsletterRegistration($account));
         }
 
@@ -115,7 +116,7 @@ class RegisterController extends Controller
     public function storePhone(Request $request)
     {
         $request->validate([
-            'terms' =>'accepted',
+            'terms' => 'accepted',
             'privacy' => 'accepted',
             'username' => [
                 new NoUppercase,
@@ -135,6 +136,9 @@ class RegisterController extends Controller
                 'unique:accounts,username',
                 new WithoutSpaces, 'starts_with:+'
             ],
+            'email' => config('app.account_email_unique')
+                ? 'nullable|email|unique:accounts,email'
+                : 'nullable|email',
             'g-recaptcha-response'  => 'required|captcha',
         ]);
 
@@ -161,7 +165,7 @@ class RegisterController extends Controller
         $account->save();
 
         $ovhSMS = new OvhSMS;
-        $ovhSMS->send($request->get('phone'), 'Your '.config('app.name').' validation code is '.$account->confirmation_key);
+        $ovhSMS->send($request->get('phone'), 'Your ' . config('app.name') . ' validation code is ' . $account->confirmation_key);
 
         Log::channel('events')->info('Web: Account created using an SMS confirmation', ['id' => $account->identifier]);
 
diff --git a/flexiapi/app/Http/Controllers/Admin/AccountController.php b/flexiapi/app/Http/Controllers/Admin/AccountController.php
index 156a992..bef8b1e 100644
--- a/flexiapi/app/Http/Controllers/Admin/AccountController.php
+++ b/flexiapi/app/Http/Controllers/Admin/AccountController.php
@@ -32,6 +32,11 @@ use App\ExternalAccount;
 use App\Http\Requests\CreateAccountRequest;
 use App\Http\Requests\UpdateAccountRequest;
 use App\Http\Controllers\Account\AuthenticateController as WebAuthenticateController;
+use App\Rules\BlacklistedUsername;
+use App\Rules\IsNotPhoneNumber;
+use App\Rules\NoUppercase;
+use App\Rules\WithoutSpaces;
+use Illuminate\Validation\Rule;
 
 class AccountController extends Controller
 {
@@ -67,6 +72,31 @@ class AccountController extends Controller
 
     public function store(CreateAccountRequest $request)
     {
+        $request->validate([
+            'username' => [
+                'required',
+                new NoUppercase,
+                new IsNotPhoneNumber,
+                new BlacklistedUsername,
+                Rule::unique('accounts', 'username')->where(function ($query) use ($request) {
+                    $query->where('domain', $this->resolveDomain($request));
+                }),
+                'filled',
+            ],
+            'dtmf_protocol' => 'nullable|in:' . Account::dtmfProtocolsRule(),
+            'email' => [
+                'nullable',
+                'email',
+                config('app.account_email_unique') ? Rule::unique('accounts', 'email') : null
+            ],
+            'phone' => [
+                'nullable',
+                'unique:aliases,alias',
+                'unique:accounts,username',
+                new WithoutSpaces, 'starts_with:+'
+            ]
+        ]);
+
         $account = new Account;
         $account->username = $request->get('username');
         $account->email = $request->get('email');
@@ -96,6 +126,31 @@ class AccountController extends Controller
 
     public function update(UpdateAccountRequest $request, $id)
     {
+        $request->validate([
+            'username' => [
+                'required',
+                new NoUppercase,
+                new IsNotPhoneNumber,
+                new BlacklistedUsername,
+                Rule::unique('accounts', 'username')->where(function ($query) use ($request) {
+                    $query->where('domain', $this->resolveDomain($request));
+                })->ignore($id),
+                'filled',
+            ],
+            'dtmf_protocol' => 'nullable|in:' . Account::dtmfProtocolsRule(),
+            'email' => [
+                'nullable',
+                'email',
+                config('app.account_email_unique') ? Rule::unique('accounts', 'email')->ignore($id) : null
+            ],
+            'phone' => [
+                'nullable',
+                'unique:aliases,alias',
+                'unique:accounts,username',
+                new WithoutSpaces, 'starts_with:+'
+            ]
+        ]);
+
         $account = Account::findOrFail($id);
         $account->username = $request->get('username');
         $account->email = $request->get('email');
diff --git a/flexiapi/app/Http/Controllers/Api/AccountController.php b/flexiapi/app/Http/Controllers/Api/AccountController.php
index c401180..aa22179 100644
--- a/flexiapi/app/Http/Controllers/Api/AccountController.php
+++ b/flexiapi/app/Http/Controllers/Api/AccountController.php
@@ -102,7 +102,9 @@ class AccountController extends Controller
             'algorithm' => 'required|in:SHA-256,MD5',
             'password' => 'required|filled',
             'domain' => 'min:3',
-            'email' => 'required_without:phone|email',
+            'email' => config('app.account_email_unique')
+                ? 'required_without:phone|email|unique:accounts,email'
+                : 'required_without:phone|email',
             'phone' => [
                 'required_without:email',
                 'prohibits:username',
@@ -241,6 +243,9 @@ class AccountController extends Controller
                 }),
                 'size:' . WebAuthenticateController::$emailCodeSize
             ],
+            'email' => config('app.account_email_unique')
+                ? 'nullable|email|unique:accounts,email'
+                : 'nullable|email',
             // For retro-compatibility
             'token' => [
                 'required_without:account_creation_token',
diff --git a/flexiapi/app/Http/Controllers/Api/Admin/AccountController.php b/flexiapi/app/Http/Controllers/Api/Admin/AccountController.php
index d90c1e9..0ded191 100644
--- a/flexiapi/app/Http/Controllers/Api/Admin/AccountController.php
+++ b/flexiapi/app/Http/Controllers/Api/Admin/AccountController.php
@@ -119,7 +119,6 @@ class AccountController extends Controller
             ],
             'algorithm' => 'required|in:SHA-256,MD5',
             'password' => 'required|filled',
-            'email' => 'email',
             'admin' => 'boolean|nullable',
             'activated' => 'boolean|nullable',
             'dtmf_protocol' => 'nullable|in:' . Account::dtmfProtocolsRule(),
@@ -127,6 +126,9 @@ class AccountController extends Controller
                 'date_format:Y-m-d H:i:s',
                 'nullable',
             ],
+            'email' => config('app.account_email_unique')
+                ? 'nullable|email|unique:accounts,email'
+                : 'nullable|email',
             'phone' => [
                 'unique:aliases,alias',
                 'unique:accounts,username',
diff --git a/flexiapi/app/Http/Controllers/Api/EmailController.php b/flexiapi/app/Http/Controllers/Api/EmailController.php
index d48cfbe..bb664b9 100644
--- a/flexiapi/app/Http/Controllers/Api/EmailController.php
+++ b/flexiapi/app/Http/Controllers/Api/EmailController.php
@@ -27,8 +27,14 @@ class EmailController extends Controller
 {
     public function requestUpdate(Request $request)
     {
+        $rules = ['required', 'email', Rule::notIn([$request->user()->email])];
+
+        if (config('app.account_email_unique')) {
+            array_push($rules, Rule::unique('accounts', 'email'));
+        }
+
         $request->validate([
-            'email' => ['required', 'email', Rule::notIn([$request->user()->email])],
+            'email' => $rules,
         ]);
         $request->user()->requestEmailUpdate($request->get('email'));
     }
diff --git a/flexiapi/config/app.php b/flexiapi/config/app.php
index 53f4627..7816461 100644
--- a/flexiapi/config/app.php
+++ b/flexiapi/config/app.php
@@ -28,6 +28,7 @@ return [
     'proxy_registrar_address' => env('ACCOUNT_PROXY_REGISTRAR_ADDRESS', 'sip.domain.com'),
     'transport_protocol_text' => env('ACCOUNT_TRANSPORT_PROTOCOL_TEXT', 'TLS (recommended), TCP or UDP'),
 
+    'account_email_unique' => env('ACCOUNT_EMAIL_UNIQUE', false),
     'consume_external_account_on_create' => env('ACCOUNT_CONSUME_EXTERNAL_ACCOUNT_ON_CREATE', false),
     'blacklisted_usernames' => env('ACCOUNT_BLACKLISTED_USERNAMES', ''),
 
diff --git a/flexiapi/resources/views/account/login/email.blade.php b/flexiapi/resources/views/account/login/email.blade.php
index 3ce619c..c917f23 100644
--- a/flexiapi/resources/views/account/login/email.blade.php
+++ b/flexiapi/resources/views/account/login/email.blade.php
@@ -7,10 +7,12 @@
         <div class="card mt-3">
             <div class="card-body">
                 {!! Form::open(['route' => 'account.authenticate.email']) !!}
-                    <div class="form-group">
-                        {!! Form::label('email', 'Email') !!}
-                        {!! Form::email('email', old('email'), ['class' => 'form-control', 'placeholder' => 'bob@example.com', 'required']) !!}
-                    </div>
+                    @if (config('app.account_email_unique') == false)
+                        <div class="form-group">
+                            {!! Form::label('email', 'Email') !!}
+                            {!! Form::email('email', old('email'), ['class' => 'form-control', 'placeholder' => 'bob@example.com', 'required']) !!}
+                        </div>
+                    @endif
                     <div class="form-group">
                         {!! Form::label('username', 'SIP Username') !!}
                         <div class=" input-group mb-3">
diff --git a/flexiapi/resources/views/api/documentation_markdown.blade.php b/flexiapi/resources/views/api/documentation_markdown.blade.php
index 13cac0c..de1f4ca 100644
--- a/flexiapi/resources/views/api/documentation_markdown.blade.php
+++ b/flexiapi/resources/views/api/documentation_markdown.blade.php
@@ -132,7 +132,7 @@ JSON parameters:
 * `password` required minimum 6 characters
 * `algorithm` required, values can be `SHA-256` or `MD5`
 * `domain` if not set the value is enforced to the default registration domain set in the global configuration
-* `email` optional if `phone` set, an email, set an email to the account
+* `email` optional if `phone` set, an email, set an email to the account, must be unique if `ACCOUNT_EMAIL_UNIQUE` is set to `true`
 * `phone` required if `username` not set, optional if `email` set, a phone number, set a phone number to the account
 
 ### `POST /accounts/with-account-creation-token`
@@ -234,7 +234,7 @@ Delete the account.
 Change the account email. An email will be sent to the new email address to confirm the operation.
 JSON parameters:
 
-* `email` the new email address
+* `email` the new email address, must be unique if `ACCOUNT_EMAIL_UNIQUE` is set to `true`
 
 ### `POST /accounts/me/password`
 <span class="badge badge-info">User</span>
@@ -258,7 +258,7 @@ JSON parameters:
 * `domain` **not configurable by default**. Only configurable if `APP_ADMINS_MANAGE_MULTI_DOMAINS` is set to `true` in the global configuration. Otherwise `APP_SIP_DOMAIN` is used.
 * `activated` optional, a boolean, set to `false` by default
 * `display_name` optional, string
-* `email` optional, string, must be an email
+* `email` optional, must be an email, must be unique if `ACCOUNT_EMAIL_UNIQUE` is set to `true`
 * `admin` optional, a boolean, set to `false` by default, create an admin account
 * `phone` optional, a phone number, set a phone number to the account
 * `dtmf_protocol` optional, values must be `sipinfo` or `rfc2833`
diff --git a/flexiapi/resources/views/parts/password_recovery.blade.php b/flexiapi/resources/views/parts/password_recovery.blade.php
index ab6907f..1f3402a 100644
--- a/flexiapi/resources/views/parts/password_recovery.blade.php
+++ b/flexiapi/resources/views/parts/password_recovery.blade.php
@@ -1,6 +1,11 @@
 @if (config('app.web_panel'))
     <p class="text-center pt-3">
-        Set or recover your password using your <a href="{{ route('account.login_email') }}">Email address</a>
+        @if (config('app.account_email_unique'))
+            Set or recover your account
+        @else
+            Set or recover your password
+        @endif
+            using your <a href="{{ route('account.login_email') }}">Email address</a>
         @if (config('app.phone_authentication'))
             or your <a href="{{ route('account.login_phone') }}">Phone number</a>
         @endif
diff --git a/flexiapi/tests/Feature/AccountApiTest.php b/flexiapi/tests/Feature/AccountApiTest.php
index 8a9aa57..53b491b 100644
--- a/flexiapi/tests/Feature/AccountApiTest.php
+++ b/flexiapi/tests/Feature/AccountApiTest.php
@@ -471,6 +471,33 @@ class AccountApiTest extends TestCase
             ]);
     }
 
+    public function testUniqueEmailAdmin()
+    {
+        $email = 'collision@email.com';
+
+        $existing = Password::factory()->create();
+        $existing->account->activated = false;
+        $existing->account->email = $email;
+        $existing->account->save();
+
+        config()->set('app.account_email_unique', true);
+
+        $admin = Admin::factory()->create();
+        $admin->account->generateApiKey();
+        $admin->account->save();
+
+        $this->keyAuthenticated($admin->account)
+            ->json($this->method, $this->route, [
+                'username' => 'hop',
+                'email' => $email,
+                'domain' => 'server.com',
+                'algorithm' => 'SHA-256',
+                'password' => '123456',
+            ])
+            ->assertStatus(422)
+            ->assertJsonValidationErrors(['email']);
+    }
+
     /**
      * /!\ Dangerous endpoints
      */
@@ -594,6 +621,18 @@ class AccountApiTest extends TestCase
         ->assertStatus(422)
         ->assertJsonValidationErrors(['username']);
 
+        // Email is now unique
+        config()->set('app.account_email_unique', true);
+
+        $this->json($this->method, $this->route.'/public', [
+            'username' => 'johndoe',
+            'algorithm' => 'SHA-256',
+            'password' => '2',
+            'email' => 'john@doe.tld',
+        ])
+        ->assertStatus(422)
+        ->assertJsonValidationErrors(['email']);
+
         $this->assertDatabaseHas('accounts', [
             'username' => $username,
             'domain' => config('app.sip_domain')
@@ -704,6 +743,7 @@ class AccountApiTest extends TestCase
     public function testChangeEmail()
     {
         $password = Password::factory()->create();
+        $otherAccount = Password::factory()->create();
         $password->account->generateApiKey();
         $newEmail = 'new_email@test.com';
 
@@ -737,6 +777,16 @@ class AccountApiTest extends TestCase
                     'new_email' => $newEmail
                 ]
             ]);
+
+        // Email already exists
+        config()->set('app.account_email_unique', true);
+
+        $this->keyAuthenticated($password->account)
+            ->json($this->method, $this->route.'/me/email/request', [
+                'email' => $otherAccount->account->email
+            ])
+            ->assertStatus(422)
+            ->assertJsonValidationErrors(['email']);
     }
 
     public function testChangePassword()