Please kindly help me to get a clearer picture of setting up correct SPF records. I know this has been discussed on the forums a lot, but more reading is only getting me more confused. The problem is that, of course, without reverse DNS and the right SPF records lots of emails are not delivered. I'm using the latest ISPConfig 3 (CentOS, perfect setup). I have a block of external IPs and a number of domains/sites for clients. Clients send mail via mail.clientdomain1.com mail.clientdomain2.com mail.clientdomain3.com etc (DNS records were made using DNS wizard) The hostname of my server is, say, server1.example.com By searching the forum I've found that I need to 1) Ensure that the reverse dns record for the IP address matches the hostname of the server. 2) Create spf records for all domain names and configure them to allow sending for the hostname of the server. As for the 1) - all emails are sent via just one IP, so I've asked my ISP to make reverse DNS for this IP, so that it would resolve to server1.example.com I hope this is OK. As for 2) - please kindly help. I understand that I have to make an SPF record for EACH of the clients' domains - and it has to be a TXT record The name, if I understand correctly, has to be: server1.example.com. As for the text, in the examples I came across there were several mechanism used: "ip4", "a", "mx", "ptr" etc - do I have to use them all, or, for example, just "mx" mechanism is enough? That is, will it be sufficient to write: "v=spf1 mx:server1.example.com -all" ? Also, at the moment "server1" at example.com is just an "A" record, do I have to make it MX also (example.com has mail.example.com as MX now)?