The mail always lands in spam

Hi

The emails always land in Spam of the email providers like Gmail, Yahoo and Hotmail.
The authenticated result in source of the email is pass.

Authentication-Results: mx.google.com;
dkim=pass header.i=@domain.com
spf=pass (google.com: domain of userl@domain.com designates xxx.xxx.xxx.xxx as permitted sender) smtp.mailfrom=user@domain.com;
dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=domain.com

The server is running from quite some time and has never involved in any Spaming or mass mailing. Neither the ip address in the black list. Mail-tester.com result shows 8.1 saing:

-1.985 PYZOR_CHECK Similar message reported on Pyzor (http://pyzor.org)
Please test a real content, test Newsletters will always be flagged by Pyzor
Adjust your message or request whitelisting (http://public.pyzor.org/whitelist/)
and

The List-Unsubscribe header is required if you send mass emails, it enables the user to easily unsubscribe from your mailing list.
Your message does not contain a List-Unsubscribe header

  1. Do I need to have any changes or add something in the headers ? If yes, how it can be done?
  2. What is the criteria of blacklisting of email from Gmail,Yahoo,Hotmail ? And how it can be improved ?

Thanks

it could be due to the type of email.
It could be beacause your reverse dns is not properly set up.
It could be a bad ipv6 configuration
It could be because your FAI has a bad config (for exemple ip are listed in DUL)
You should test your server with http://multirbl.valli.org/lookup/