<?php

function setEmail($stringMail)
    {
        $nstringMail = preg_replace('/\;/',',', $stringMail);
        $nstringMail = preg_replace('/\v+/',',', $nstringMail);
        $nstringMail = preg_replace('/\t+/',',',  $nstringMail);
        $nstringMail = preg_replace('/\n+/',',', $nstringMail);
        $nstringMail = preg_replace('/\,\,/',',', $nstringMail);
        $nstringMail = preg_replace('/\s+/','', $nstringMail);
        
            $dataEmail = explode(',', $nstringMail);
           if (!empty($dataEmail)) {
               foreach ($dataEmail as $stringValue) {
               	  if (filter_var($stringValue, FILTER_VALIDATE_EMAIL)) {
                         $emails[] = $stringValue;
                  }
               }
           }
        array_unique($emails);
        return $emails;
    }

$saida = setEmail('exemplo1@email.com; exemplo2@email.com; exemplo3@email.com; exemplo4@email.com; exemplo5@email.com; exemplo6@email.com;');

//echo "<pre>";
print_r($saida);