Got the same issue. Everything was setup properly. SPF, dkim, dmarc was all good. Server IP wasn’t in any blocklists. But my messages would still fall in spam with Gmail.

Ended up setting sendgrid as a relay and all is good now.

Kind of both. His server has a mirror of the community. When he comments it gets saved on his server and the his server communicates with the original server. In turn the original server also communicates his comment with other federated servers.