The Sender Policy Framework (SPF) is a method of fighting spam. As more time passes, this protocol will be used as one of the standard methods of fighting spam on the Internet. An SPF record is a TXT record that is part of a domain's DNS zone file. The TXT record specifies a list of authorized host names/IP addresses where mail can originate from for a given domain name. Once this entry is placed within the DNS zone, no further configuration is necessary to take advantage of servers that incorporate SPF checking into their anti-spam systems. This SPF record is added the same way as a regular A, MX, or CNAME record.
Adding an SPF record to your zone file is the best way to stop spammers from using this technique with your domain. An SPF record will eliminate a high proportion of the bouncebacks you've been getting, because other mail providers will reject the email immediately without sending a bounceback to the (spoofed) reply-to address. While the SPF record is not 100% effective, because not all mail providers check for it, you should notice a drastic decrease in the amount of bouncebacks you receive.
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