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Sender Permitted From

Sender Permitted From is an extension to SMTP, also called SMTP+SPF, designed to help relieve spam. It works by letting a domain specify who is eligible to transmit e-mail for itself, using special codes in the TXT DNS records.

The exact specifications may change, but as of writing, the records are laid out like this (in typical DNS-syntax): IN TXT "v=spf1 mx ptr default=deny"

"v=" defines the version of SPF used, the following words provides the methods to use to determine if a domain is eligible to send mail, and the "default=" defines how to treat non-matching hostnames.

The following methods are defined:

SPF only keeps spammers from forging the domain names given in the From-addresses of an email, it does not keep them from sending from their own domains.

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