SPF
Framework to prevent forgery of email-sender address
The Sender Policy Framework (SPF) allows software to identify emails that have forged sender addresses
before they enter a system.
The normal SMTP protocol allows anyone to send an email with an arbitrary 'From' address, a method that
is widely used by spammers to prevent their messages from being filtered and to make
their emails appear genuine.
If a domain supports SPF, it stores in its DNS entries those IP addresses that
are allowed to send email from the domain. A receiving SMTP server can compare the IP address that tries
to send an email with the allowed addresses of the domain(s) provided in the HELO and
MAIL FROM commands.
SPF has two benefits: it helps the receiving mail server block spam before it enters the system
and it helps reduce backscatter spam for users on the domain that is being forged.
SPF does not block spammers who use their own domains to send email, neither will it block
spammers who use legitimate email services, such as webmail, to send their spam or users who pretend to be
another user on the same domain. In theory it is also possible to use SPF for DoS attacks on
DNS servers.
Related web links
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