Hello everyone, Here's the links from my yesterday talk/rant/open-ended question thingy. Error message gmail gives you when you try to use IPv6 with no proper PTR records -- https://support.google.com/mail/answer/81126?p=ipv6_authentication_error&rd=1#authentication Instructions on setting up reverse DNS with NSD, which in my case is not relevant because I don't control the IP block and my ISP needs to do that for me -- https://www.sixxs.net/wiki/NSD#Zone_configuration Subnet calculator that also works with IPv6, and will definitely will help you to keep your sanity in case you also need to work with IPv6 -- http://www.gestioip.net/cgi-bin/subnet_calculator.cgi Myles sent me a link on how to configure PTR using Linode manager, which basically answers the question -- https://www.linode.com/docs/networking/dns/setting-reverse-dns Debian Administrator's Handbook -- https://debian-handbook.info/ Also to answer Scott's question if the book has a section on mail server, indeed it does. I assumed the book would go over Exim setup, as it is the default mail server in Debian, but apparently Postfix is documented instead -- https://debian-handbook.info/browse/stable/network-services.html#sect.smtp-m... Thanks, Alex.