public MailMessage ComposeMail(string mailFrom,string mailTo,string copyTo,byte[] docFile)
{
    var mail = new MailMessage();

    mail.From = new MailAddress(mailFrom);

    mail.To.Add(new MailAddress(mailTo));
    mail.Body = "mail with attachment";

    System.Net.Mail.Attachment attachment;

    //Attach the byte array as .docx file without having to store it first as a file on disk?
    attachment = new System.Net.Mail.Attachment("docFile");
    mail.Attachments.Add(attachment);

    return mail;
}