"Rand" == Rand Wacker <rand(_at_)sendmail(_dot_)com> writes:
Rand> The 480 byte limit is a limit of UDP. The potential to have
Rand> to fall back to a TCP call-back connection is pretty scary
Rand> to sites that receive billions of messages a day.
It's not a limit of UDP, though it stems from the 512 byte limit that
RFC1035 places on DNS over UDP.
EDNS0 (RFC2535) provides a mechanism for sending larger DNS
transactions over UDP. RFC3226 (which is also referenced by Sender
ID) says that EDNS0 implementations MUST allow at least 1220 bytes,
and SHOULD allow at least 4000 bytes.
-roy