Where can I get a normal step-by-step manual for setting up DKIM for Postfix under Ubuntu Server 16.04?

Question

gmail

The situation is more than standard:
- It is necessary that letters from the server (VPS under Ubuntu 16.04) pass verification normally on Yandex and Gmail.
SPF adjusted - norms. I tried to set up DKIM - it doesn't work (-: I used as a manual:
https://www.dmosk.ru/instruktions.php?object=dkim-... and additionally:
https://flops.ru/kb/knowledge- base/nastroyka-dkim-...
tried this and that - doesn't work - Gmail doesn't recognize my DKIM
# opendkim-testkey -d mysite.ru -s relay -vvv
.

opendkim-testkey: using default configfile /etc/opendkim.conf
opendkim-testkey: checking key 'relay._domainkey.mysite.ru'
opendkim-testkey: key not secure
opendkim-testkey: key OK

In general, I want to raise this matter in the air somehow.
I will be glad to advice.

Answer 1

I configured DKIM on Proxmox Gateway according to the manuals
https://wiki.debian.org/opendkim
https://flops.ru/kb/knowledge-base/nastroyka-dkim-...

Answer 2

I think everything is ok with you.
opendkim-testkey: key not secure only means that dnssec is not configured on your dns. And so, in fact, the last line is the result of checking the key.