I have done a form that when sending to the mail it shows me the following error 
here I share the code of the form
<form class="form-grp clearfix grpelem" id="widgetu12198" method="post" enctype="multipart/form-data" action="localhost/new_arreglosya/scripts/form-u12198.php">
<!-- none box -->
<div class="fld-grp clearfix grpelem" id="widgetu12223" data-required="true">
<!-- none box -->
<label class="fld-label actAsDiv clearfix grpelem" id="u12224-4" for="widgetu12223_input">
<!-- content -->
<span class="actAsPara">Nombre</span>
</label>
<span class="fld-input NoWrap actAsDiv clearfix grpelem" id="u12225-4"><!-- content -->
<input class="wrapped-input" type="text" spellcheck="false" id="widgetu12223_input" name="custom_U12223" tabindex="1"/>
</span>
</div>
<div class="fld-grp clearfix grpelem" id="widgetu12207" data-required="true" data-type="email">
<!-- none box -->
<label class="fld-label actAsDiv clearfix grpelem" id="u12210-5" for="widgetu12207_input">
<!-- content -->
<span class="actAsPara"> ¿Donde se realizará el trabajo?</span>
<span class="actAsPara" id="u12210-3"> </span>
</label>
<span class="fld-input NoWrap actAsDiv clearfix grpelem" id="u12209-4"><!-- content -->
<input class="wrapped-input" type="email" spellcheck="false" id="widgetu12207_input" name="Email" tabindex="2"/>
</span>
</div>
<div class="clearfix grpelem" id="u12220-4">
<!-- content -->
<p>Submitting Form...</p>
</div>
<div class="clearfix grpelem" id="u12221-4">
<!-- content -->
<p>The server encountered an error.</p>
</div>
<div class="clearfix grpelem" id="u12211-4">
<!-- content -->
<p>Form received.</p>
</div>
<button class="submit-btn NoWrap clearfix grpelem" id="u12222-4" type="submit" value=" enviar" tabindex="5">
<!-- content -->
<div style="margin-top:-15px;height:15px;">
<p> enviar</p>
</div>
</button>
<div class="fld-grp clearfix grpelem" id="widgetu12199" data-required="true">
<!-- none box -->
<label class="fld-label actAsDiv clearfix grpelem" id="u12202-4" for="widgetu12199_input">
<!-- content --><span class="actAsPara">Celular</span>
</label>
<span class="fld-input NoWrap actAsDiv clearfix grpelem" id="u12201-4"><!-- content --><input class="wrapped-input" type="tel" spellcheck="false" id="widgetu12199_input" name="custom_U12199" tabindex="3"/><label class="wrapped-input fld-prompt" id="widgetu12199_prompt" for="widgetu12199_input"><span class="actAsPara">Introducir Celular</span></label>
</span>
</div>
<div class="fld-grp clearfix grpelem" id="widgetu12212" data-required="true">
<!-- none box -->
<label class="fld-label actAsDiv clearfix grpelem" id="u12215-4" for="widgetu12212_input">
<!-- content --><span class="actAsPara">Mail:</span></label>
<span class="fld-input NoWrap actAsDiv clearfix grpelem" id="u12214-4"><!-- content --><input class="wrapped-input" type="tel" spellcheck="false" id="widgetu12212_input" name="custom_U12212" tabindex="4"/><label class="wrapped-input fld-prompt" id="widgetu12212_prompt" for="widgetu12212_input"><span class="actAsPara">Introducir mail</span></label>
</span>
</div>
</form>
and here the method that receives the data
require_once('form_process.php');
$form = array(
'subject' => 'Envío de Pintura, Interiores, Blanco, Con Material',
'heading' => 'Envío de nuevo formulario',
'success_redirect' => '',
'resources' => array(
'checkbox_checked' => 'Marcada',
'checkbox_unchecked' => 'No marcada',
'submitted_from' => 'Formulario enviado desde el sitio web: %s',
'submitted_by' => 'Dirección IP del visitante: %s',
'too_many_submissions' => 'Se han realizado recientemente demasiados envíos a través de esta IP',
'failed_to_send_email' => 'Error al enviar el correo electrónico',
'invalid_reCAPTCHA_private_key' => 'Clave privada de reCAPTCHA no válida.',
'invalid_reCAPTCHA2_private_key' => 'Clave privada de reCAPTCHA 2.0 no válida.',
'invalid_reCAPTCHA2_server_response' => 'Respuesta de servidor de reCAPTCHA 2.0 no válida.',
'invalid_field_type' => 'Tipo de campo desconocido: %s.',
'invalid_form_config' => 'El campo \'%s\' contiene una configuración no válida.',
'unknown_method' => 'Método de solicitud de servidor desconocido'
),
'email' => array(
'from' => '[email protected]',
'to' => '[email protected]'
),
'fields' => array(
'custom_U12223' => array(
'order' => 1,
'type' => 'string',
'label' => 'Nombre',
'required' => true,
'errors' => array(
'required' => 'El campo \'Nombre\' es obligatorio.'
)
),
'Email' => array(
'order' => 2,
'type' => 'email',
'label' => ' ¿Donde se realizará el trabajo?',
'required' => true,
'errors' => array(
'required' => 'El campo \' ¿Donde se realizará el trabajo?\' es obligatorio.',
'format' => 'El campo \' ¿Donde se realizará el trabajo?\' contiene un correo electrónico no válido.'
)
),
'custom_U12199' => array(
'order' => 3,
'type' => 'string',
'label' => 'Celular',
'required' => true,
'errors' => array(
'required' => 'El campo \'Celular\' es obligatorio.'
)
),
'custom_U12212' => array(
'order' => 4,
'type' => 'string',
'label' => 'Mail',
'required' => true,
'errors' => array(
'required' => 'El campo \'Mail\' es obligatorio.'
)
)
)
);
process_form($form);
is done in php and html without any type of framewor or special configuration, only Muse