Outlook blocks my PHPmailer but they deny it

Question

I use phpmailer to deliver important information to my clients about their interactions with the site, security codes, etc. The mailer uses a gmail account I set up and works just fine emailing other gmail accounts. Hotmail has never worked, and my work outlook account received one or two emails before also going dark.

I emailed the header information to outlook but they state there's no block on the IP and plugging it into their automated system returns google postmaster (which they automatically e-mail instructions to for helping me out. I don't have access to the google postmaster account, so obviously I don't receive them).

My question is what do I do now. Half of my clients use outlook and I need to access them. Outlook customer service has been less helpful than a magic 8 ball and keep referring me back to their smart network data services, which keeps sending info to google postmaster. When I tell them this, they tell me there's no block on the IP and send me the same links. I'm stuck in their loop and just want them to let my e-mails get through!

EDIT:
I believe it has to do with the PHPmailer, because if I send the e-mail directly from the google account, it gets through:

                require "../mailer/PHPMailerAutoload.php";
                    $mail = new PHPMailer;

                    $mail->isSMTP();                                      // Set mailer to use SMTP
                    $mail->Host = 'smtp.gmail.com';                          // Specify main and backup SMTP servers
                    $mail->SMTPAuth = true;                               // Enable SMTP authentication

                    $mail->Username = $outputMail['email'];              // SMTP username
                    $mail->Password = $outputMail['pass'];               // SMTP password
                    $mail->SMTPSecure = 'tls';                            // Enable TLS encryption, `ssl` also accepted
                    $mail->Port = 587;                                    // TCP port to connect to

                    $mail->AddReplyTo("[email protected]");
                    $mail->From = "[email protected]";
                    $mail->FromName = "My Business";
                    $mail->addAddress($email);      // Add a recipient

                    $mail->isHTML(true);                                  // Set email format to HTML

Answer 1

So, after a LOT of digging, it turns out it was the PHPmailer, so I'll leave this here for anyone that needs it. Outlook / hotmail apparently have an EXTREMELY high spam filter, and mail that has a AddReplyTo or FROM section (as I had above) or does not have an 'unsubscribe' link can be filtered out. Removing that completely solved my problem.