[Ralf Doeblitz]
If you are using dialup lines with a dynamically assigned ip address,
your ISP should publish a matching SPF record that you can include or
redirect to in your own SPF record.
If you have a static allocation, your ISP should notify you of any
changes well ahead of time (at least one week, better two or more) so
you can modify your DNS data accordingly.
Current Internet business is not simply ISP and client.
ISP can inform their reseller on address changes, but reseller can forget to
notify you/use your outdated email or simply ignore ISP warning, as they
will find it's not valuable.
As well your company administrator can be on two weeks Hawaiian Vacation.
Do you wish to create SPF records change burden simply because your ISP
decided to optimize their network?
BTW, single change in ISP IP allocation requires you to change your DNS zone
at least twice.
Once to list both old and new IP ranges, at second to remove old IP range.
SPF requires current and relevant information about complete mail routing
path to be stored in DNS.
This make impossible for ISPs to optimize their mail flow by using
additional outgoing MTA. For example Ukrainian ISP will be unable to use
dedicated Russian server to optimize traffic pattern for emails like
user(_at_)domain(_dot_)RU
SPF will not allow this because this will require ISP clients to list and
maintain Russian server address in their zone.
Adding additional Germany (*(_at_)*(_dot_)de, UK) or US servers will require all
clients notified and forced to update their data. Or such an optimization
must perform SPF checks in advance - costly process :-(
Or take a read section 6.4 (Roving users scenario) in DomainKeys draft.
--
Andriy G. Tereshchenko
TAG Software
Odessa, Ukraine
http://www.24.odessa.ua