First of all, I mus say this forum is a must for the beginners. I'm really learning a lot. Thank you all. But I have a BIG problem with my emails, and I will tell you now:
1) When I fill the contact form on my website, I receive an e-mail (on my gmail account, as I configured). The problem is the e-mail comes with a question-mark and the information that Gmail couldn't verify mydomain is sending the message or some spammer. Curious is, if I send 3 or 4 contact forms, the first two emails comes with that information, and the other don't. That's one problem.
2) When I compose an e-mail message (via Roundcube or Usermin) and send it to Gmail, the message goes directly to SPAM folder. To the Hotmail, same happens. I couldn't test with Yahoo, but I believe the same will happen.
3) When I try to send an e-mail to some other domains, sometimes I can send, sometimes I can't. The last "undelivered" message I got the header message:
Reporting-MTA: dns; amantesdocarnavalsp.com.br
X-Postfix-Sender: rfc822; email@example.com
Arrival-Date: Tue, 5 Jul 2016 18:51:24 -0400 (EDT)
Final-Recipient: rfc822; firstname.lastname@example.org
Remote-MTA: dns; spmexp-mx-02.cloudexchange.com.br
Diagnostic-Code: smtp; 550 High probability of spam
4) Some people told me they can't send me e-mail, because they got the mail undelivered, but I can't see the header of them.
Debian 8. DKIM activated, DNS records ok.
Please, someone help me.