in my CRM online system I control ingoing mails with IMAP protocol. Now I\'m making sending mails with phpmailer and SMTP protocol. Everything is ok but I have one wierd thi
If either of these two points are not true, the short answer is "You can't". In short, really it's down to the mail provider, not your code.
As much as I hate M$, Exchange is one place where they really have got things right - if you are using an Exchange server, all of this is handled for you.