diff --git a/interface/web/mail/form/mail_domain.tform.php b/interface/web/mail/form/mail_domain.tform.php
index 4a042abf2e354cf41f2e688862a234ba2f09e60b..fac30541f454847d4e14006301fd7af9de1a5ec6 100644
--- a/interface/web/mail/form/mail_domain.tform.php
+++ b/interface/web/mail/form/mail_domain.tform.php
@@ -130,9 +130,9 @@ $form["tabs"]['domain'] = array (
 			'default'       => 'default',
 			'value'         => 'default',
 			'width'  => '20',
-			'maxlength' => '63',
+			'maxlength' => '126',
 			'validators' => array (  0 => array (   'type' => 'REGEX',
-					'regex' => '/^(?=.*[a-z])[a-z0-9]{1,63}$/',
+					'regex' => '/^[a-z0-9]{1,63}(?:\.[a-z0-9]{1,63})?$/',
 					'errmsg'=> 'dkim_selector_error'),
 			),
 		),
diff --git a/interface/web/mail/lib/lang/de_mail_domain.lng b/interface/web/mail/lib/lang/de_mail_domain.lng
index 1a64a442313cc21dd6adeb0b895aba31729f33dc..0a972caa42f76e7bf8d5abf467f826ec157bd18d 100644
--- a/interface/web/mail/lib/lang/de_mail_domain.lng
+++ b/interface/web/mail/lib/lang/de_mail_domain.lng
@@ -17,7 +17,7 @@ $wb['limit_maildomain_txt'] = 'Die maximale Anzahl an E-Mail Domains für Ihr Ko
 $wb['policy_txt'] = 'Spamfilter';
 $wb['no_policy'] = '- nicht aktiviert -';
 $wb['dkim_selector_txt'] = 'DKIM-Selector';
-$wb['dkim_selector_error'] = 'Ungültiger DKIM-Selector.  Verwenden Sie nur max. 63 alphanumerische Zeichen (a-z oder 0-9)';
+$wb['dkim_selector_error'] = 'Ungültiger DKIM-Selector. Verwenden Sie nur max. 63 alphanumerische Zeichen (a-z oder 0-9), gefolgt von einem optionalen Punkt und weiter 63 alphanumerischen Zeichen.';
 $wb['dkim_settings_txt'] = 'DomainKeys Identified Mail (DKIM)';
 $wb['error_not_allowed_server_id'] = 'Chosen server is not allowed for this account.';
 $wb['relayhost_txt'] = 'Relayhost';
diff --git a/interface/web/mail/lib/lang/en_mail_domain.lng b/interface/web/mail/lib/lang/en_mail_domain.lng
index 39e22f75b6219addb8f7ceede6d49928934e595c..fe4cad303f8253de066f5edb2b24a831c78e99c9 100644
--- a/interface/web/mail/lib/lang/en_mail_domain.lng
+++ b/interface/web/mail/lib/lang/en_mail_domain.lng
@@ -19,7 +19,7 @@ $wb['policy_txt'] = 'Spamfilter';
 $wb['no_policy'] = '- not enabled -';
 $wb['error_not_allowed_server_id'] = 'Chosen server is not allowed for this account.';
 $wb['dkim_selector_txt'] = 'DKIM-Selector';
-$wb['dkim_selector_error'] = 'Invalid DKIM-Selector. Use only lower-case alphanumeric characters (a-z or 0-9) up to 63 chars';
+$wb['dkim_selector_error'] = 'Invalid DKIM-Selector. Use only lower-case alphanumeric characters (a-z or 0-9) up to 63 chars, optional followed by a period and by another string of no more than 63 lower-case alphanumeric characters.';
 $wb['relayhost_txt'] = 'Relayhost';
 $wb['relayhost_user_txt'] = 'Relayhost User';
 $wb['relayhost_password_txt'] = 'Relayhost Password';
diff --git a/interface/web/mail/lib/lang/es_mail_domain.lng b/interface/web/mail/lib/lang/es_mail_domain.lng
index bd23b94191934ba8d40d236b56e11b37894ca30b..4a3feb7c8b9132b80312aee885d526d6676f45b5 100644
--- a/interface/web/mail/lib/lang/es_mail_domain.lng
+++ b/interface/web/mail/lib/lang/es_mail_domain.lng
@@ -6,7 +6,7 @@ $wb['dkim_generate_txt'] = 'Generar clave privada DKIM';
 $wb['dkim_private_key_error'] = 'Clave privada DKIM no válida';
 $wb['dkim_private_txt'] = 'Clave privada DKIM';
 $wb['dkim_public_txt'] = 'Clave pública DKIM\nsólo para información';
-$wb['dkim_selector_error'] = 'Selector DKIM no válido. Use como máximo 63 caracteres alfanuméricos en minúsculas (a-z o 0-9)';
+$wb['dkim_selector_error'] = 'Selector DKIM inválido. Utilice <subdominio(.subdominio)>. El subdominio tiene un máximo de 63 caracteres en minúsculas <a-z y 0-9> y el segundo subdominio es opcional';
 $wb['dkim_selector_txt'] = 'Selector DKIM';
 $wb['dkim_settings_txt'] = 'Correo Identificado por Claves de Dominio (DKIM)';
 $wb['dkim_txt'] = 'Activar DKIM';