253 (visible) characters actually, 255 is the max for the data in the query,
you can't put a fqdn thats contains 255 visible characters into a dns query,
it's too big (by 2 bytes)
eg; machine.domain.xyz
as text [machine.domain.xyz] it's 18 bytes long but in a query packet
[<0x07>machine<0x06>domain<0x03>xyz<0x00>] it's 20 bytes long
my take is that any expansion that violates those limits should get treated
the same as an invalid domain, and if treated as such (PERMFAIL) it would
make them correct the problem a lot quicker. although i suppose you could
be nice and treat it as a non-existant domain instead.
i don't like the idea of chopping bits off until it fits, and i actually
can't belive that it's ended up in the spec. if it doesn't fit, it doesn't
fit and it should be changed (at the senders SPF record) so that it does.
----- Original Message -----
From: "Roger Moser" <Roger(_dot_)Moser(_at_)rama(_dot_)pamho(_dot_)net>
To: <spf-discuss(_at_)v2(_dot_)listbox(_dot_)com>
Sent: Saturday, November 27, 2004 2:30 AM
Subject: [spf-discuss] domain name labels are limited to 63 characters
You probably now that labels in domain names are limited to 63 characters
and the whole domain name is limited to 255 characters.