Moved server and now emails are not displaying correctly in email client

Hi guys,

Bit of a strange one here. My HTML emails have sent fine for years however we recently changed server and the emails do not display properly in outlook however they are fine in hotmail etc

They are displaying like this

Content-Type: text/plain; charset=ISO-8859-1

Content-Transfer-Encoding: base64

CkNCVCBCb29raW5nIENvbmZpcm1hdGlvbgoKKiB7cGFkZGluZzowcHg7bWFyZ2luOjBweDt9CmJv

ZHkge2ZvbnQtZmFtaWx5OmFyaWFsO21hcmdpbi10b3A6MjBweDtmb250LXNpemU6MC44ZW07fQph

IHtjb2xvcjojMTAzOTZCO30KI3BiIHt3aWR0aDo2NDBweDt9CiNwZiB7d2lkdGg6NjQwcHg7Ym9y

Here is the code i am using

function sendHTMLemail($HTML,$from,$to,$subject)
{
// First we have to build our email headers
// Set out "from" address

    $headers = "From: $from\\r\
"; 

// Now we specify our MIME version

    $headers .= "MIME-Version: 1.0\\r\
"; 

// Create a boundary so we know where to look for
// the start of the data

    $boundary = uniqid("HTMLEMAIL"); 
    
// First we be nice and send a non-html version of our email
    
    $headers .= "Content-Type: multipart/alternative;".
                "boundary = $boundary\\r\
\\r\
"; 

    $headers .= "This is a MIME encoded message.\\r\
\\r\
"; 

    $headers .= "--$boundary\\r\
".
                "Content-Type: text/plain; charset=ISO-8859-1\\r\
".
                "Content-Transfer-Encoding: base64\\r\
\\r\
"; 
                
    $headers .= chunk_split(base64_encode(strip_tags($HTML))); 

// Now we attach the HTML version

    $headers .= "--$boundary\\r\
".
                "Content-Type: text/html; charset=ISO-8859-1\\r\
".
                "Content-Transfer-Encoding: base64\\r\
\\r\
"; 
                
    $headers .= chunk_split(base64_encode($HTML));  

// And then send the email ....

    mail($to,$subject,"",$headers);
    mail($to2,$subject,"",$headers);    
}

Any help would be much appreciated