I have ispconfig3 server Same machine runs my custom dns and my mail server I host multiple domains and sub domains on this machine. Just like to keep out some intruder mail from using my domains/subdomain with spf txt . What TXT is recommended for hosting server to keep out of trouble? I'm after to send mail for all domains (virtual or FQ domains that i host on my server/network) but do not allow to send for no one past that. plese let me have the txt spf code and if i should place them in each domain dns txt record or only in my main mail server/domain dns txt record. Thank you so much. Ispconfig3 is nice tool.