I finally archive this, apperantly q2a does not support the use of web services natively, but I found a workarround editing the file qa-src/Notification/Email.php inside the function sendMessage adding the following code:
$location = "<webserviceURL>";
$subjectMail = strtr($subject, $fullsubs);
$userEmail = $this->email;
$bodyContent = htmlspecialchars(nl2br($bodyPrefix . strtr($body, $fullsubs))); // nl2br is neccesary to preserve line breaks and the htmlspecialchars escape the caracters
$mensaje = "<Msg>
<FROM>Q2A</FROM>
<TO>$userEmail</TO>
<SUBJECT>$subjectMail</SUBJECT>
<TEXT>$bodyContent</TEXT>
</Msg>"; // This line contains the message format used in my particular webservice, it is neccesaey to replace the characters <,> with < >
$request = "<?xml version=\"1.0\" encoding=\"utf-8\"?>
<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">
<soap:Body>
<Send xmlns=\"<sendOperationURL>\">
<MsgEntry>$mensaje</MsgEntry>
</Send>
</soap:Body>
</soap:Envelope>";
$headers = [
"Method: POST",
"Authorization: <auth header if neccesary>", // Depending on the web service the auth could be managed different
"Content-Type: text/xml; charset=utf-8",
"Host: <host name>",
"SOAPAction: <sendOperationURL>/<operation action>"
];
$ch = curl_init($location);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $request);
curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
// I get some errors with SSL so I added the following two lines
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
$response = curl_exec($ch);
So I manually send the mail using culr.