problem between maxbulk mailer and free

when I send an email to a gmail address and a free address from the website of my access provider (, formerly, all the mails arrive at their destination.
On the other hand, when I do the same thing from maxbulk mailer, the mail arrives at the gmail recipient, but not at the free recipient: the error message states that the message sent to free is marked as spam.
Why ?
Please note that I use the port (465), TLS and SSL recommended by
I sent the same email with different software and I already tested this email with mail tester. it is considered spam only when I send it with maxbulk mailer to a free recipient. how to correct this?