PHP Mail stops working without me editing the code

Question

I have a problem with my PHP Mail. It stops working from time to time without me even touching the code. I have a script which checks if required forms are empty. This script works. But if I fill in all the required fields I should get a text which says "Your mail was successfully sent" but I don't. But if I edit my code by just moving a bit of text some lines down and back to the original position again it works, for a while. It's often under the night it stops working. Can it be the server that is causing trouble or is it my code that I posted below?

<?php

if(isset($_POST['submit'])){

$namn = strip_tags($_POST['namn']);
$foretag = strip_tags($_POST['foretag']);
$adress = strip_tags($_POST['adress']);
$postnr = strip_tags($_POST['postnr']);
$ort = strip_tags($_POST['ort']);
$telefon = strip_tags($_POST['telefon']);
$epost = strip_tags($_POST['epost']);
$meddelande = strip_tags($_POST['meddelande']);

function check_required_fields($required_array){
    $field_errors = array();
    foreach($required_array as $fieldname){
        if ((!isset($_POST[$fieldname])) || (empty($_POST[$fieldname]))){ 
            if($_POST[$fieldname] != '0'){
                $field_errors[] = $fieldname; 
            }
        }
    }
    return $field_errors;
}

$errors = array();
$required_fields = array('namn', 'telefon', 'meddelande');
$errors = array_merge($errors, check_required_fields($required_fields));

if(empty($errors)){

$meddelande=nl2br($meddelande);

if(empty($foretag)){ $foretag='-'; }
if(empty($adress)){ $adress='-'; }
if(empty($postnr)){ $postnr='-'; }
if(empty($ort)){ $ort='-'; }
if(empty($epost)){ $epost='-'; }

$body = 
"
Namn: <b>". $namn ."</b><br />
Företag: <b>". $foretag ."</b><br />
Adress: <b>". $adress ."</b><br />
Postnr: <b>". $postnr ."</b><br />
Ort: <b>". $ort ."</b><br />
Telefon: <b>". $telefon ."</b><br />
E-post: <b>". $epost ."</b><br /><br />
Meddelande: <b><br />". $meddelande
;

$headers = "From: $namn <webmaster@allflytt.com>\r\n";
$headers .= "Content-type: text/html; charset=utf-8\r\n";
$headers .= "X-Mailer: PHP v".phpversion();

$success = mail('info@allflytt.com', 'Meddelande', $body, $headers);

}

}

?>

    <form method="post" action="<?php echo htmlentities($_SERVER['PHP_SELF']); ?>">
    
            <?php
                if(!empty($errors)){
                    echo "<p class=\"field_error\">De rödmarkerade fälten måste fyllas i.</p>";
                }
            ?>
            
            <?php
                if(empty($errors) && $success){
                    echo "<p class=\"p_success\">Tack för ditt meddelande! Vi kommer att besvara det inom kort.</p>";
                }
            ?>
    
    <p>
        <label for="namn">
        <?php if(!empty($errors)){if(in_array("namn", $errors)){echo "<span class=\"field_error\">";}}?>Namn: *<?php if(!empty($errors)){if(in_array("namn", $errors)){echo "</span>";}} ?>
        </label><br />
        <input type="text" name="namn" id="namn" class="text" tabindex="15" value="<?php if(!empty($errors)){ echo $namn; } ?>" />
            <br />
        <label for="foretag">Företag:</label><br />
        <input type="text" name="foretag" id="foretag" class="text" tabindex="20" value="<?php if(!empty($errors)){ echo $foretag; }?>" />
            <br />
        <label for="adress">Adress:</label><br />
        <input type="text" name="adress" id="adress" class="text" tabindex="30" value="<?php if(!empty($errors)){ echo $adress; } ?>" />
            <br />
        <label for="postnr">Postnummer:</label><br />
        <input type="text" name="postnr" id="postnr" class="text_medium" tabindex="40" value="<?php if(!empty($errors)){ echo $postnr; } ?>" />
            <br />
        <label for="ort">Ort:</label><br />
        <input type="text" name="ort" id="ort" class="text" tabindex="50" value="<?php if(!empty($errors)){ echo $ort; } ?>" />
            <br />
        <label for="telefon">
        <?php if(!empty($errors)){if(in_array("telefon", $errors)){echo "<span class=\"field_error\">";}}?>Telefon: *<?php if(!empty($errors)){if(in_array("telefon", $errors)){echo "</span>";}} ?>
        </label><br />              
        <input type="text" name="telefon" id="telefon" class="text" tabindex="60" value="<?php if(!empty($errors)){ echo $telefon; } ?>" />
            <br />
        <label for="epost">E-post:</label><br />                
        <input type="text" name="epost" id="epost" class="text" tabindex="70" value="<?php if(!empty($errors)){ echo $epost; } ?>" />
            <br />
        <label for="meddelande">
        <?php if(!empty($errors)){if(in_array("meddelande", $errors)){echo "<span class=\"field_error\">";}}?>Meddelande: *<?php if(!empty($errors)){if(in_array("meddelande", $errors)){echo "</span>";}} ?>
        </label><br />              
        <textarea name="meddelande" id="meddelande" class="textarea" tabindex="80"><?php if(!empty($errors)){ echo $meddelande; } ?></textarea>
            <br />  
        <input type="submit" name="submit" value="Skicka" class="submit" />
    </p>

    </form>

Answer 1

Problem solved. Changed to a new server host. No issues any more!