In your SPF record, reference the dynamic IP address using the hostname, for example: <tt>a:dynamicip.example.com</tt>.
| | In your SPF record, reference the dynamic IP address using the hostname, for example: <tt>a:name.example.com</tt>.
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However, with any dynamic service there is always a risk that things will be out of sync. As an example, if you send a message to a server that is backlogged and then that server does an SPF check as part of its post-SMTP spam filtering process (SpamAssassin does this) somewhat later and your IP address has changed in the interval, then the SPF check will fail. Operating a mail server on a dynamic IP address is problematic for a number of (mostly non-SPF) reasons. This is only one.
Also note that many ISPs use Spamhaus' [[http://www.spamhaus.org/pbl/|Policy Block list]] (or, like AOL, their own list) and do not accept mail from dynamic IP addresses.
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