Email goes in spam when I send it via others SMTP server

Question

I\'m using PHP Swift_mailer library to send emails to my customers\' clients from behalf of customers. I use their SMTP server, port, login, pass:

$transport = S         


        

Answer 1

It's because of your SMTP server. Not the server that runs PHP. The SMTP server is blocked by the destination mail server. For making sure of it, if you change your settings (in PHP code) with Gmail server, it won't go to the spam folder any more.

It worked pretty well for a few months, but now the emails started to appear in a Spam folder for some of my customers?

That's because the destination mail server has added your SMTP server to their blacklist.