Sometimes Gmail marks as spam an email I receive that is a reply to something I wrote. The reason it presents is
Lots of messages from mydomain.com were identified as spam in the past. My emails are sent via my domain host, and are received back also through it, forwarded to my gmail account, this way:
Sender -> firstname.lastname@example.org -> email@example.com
Some months ago I asked my host about this and they said they added SPF and DKIM, but it's still happening.
My domain is not blacklisted on any site I looked in (spamhaus.org, senderbase.org, email-checker.com, mxtoolbox.com). On mail-tester.com it claims my message is not signed with DKIM, but that is for a message I'm sending.
What should I do? Can I contact Google about this? Haven't found any way of doing it.
Here's the full email header: https://pastebin.com/AvfeaStQ
Here's how it look on Gmail: