Re: Add PostgreSQL Discord to website?

If there are "official" channels (e.g. like the IRC ones) then sure. Otherwise it should be noted as being unofficial community channels run by third parties. Maybe grouping all such things under one place with a common, "Third party community sites..." heading.

FYI, the Slack link on the mailing list site goes to https://postgres-slack.herokuapp.com/ but it's a 404.

It was probably running on the Heroku free tier and stopped when they shut down their free tier at the end of last year.

Adding Denish to this thread as the earliest mention I could find of that link in the mailing lists was from him.