Raymond Neeves wrote:
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)
That is true according to RFC 1034 and 1035. So in the SPF specification
"255" should be replaced with "253":
When the result of macro expansion is used in a domain name query, if
the expanded domain name exceeds 253 characters, the left side is
truncated to fit, by removing successive subdomains until the total
length does not exceed 253 characters. This is required because in DNS
packets the total length of a domain name (the sum of all label octets
and label lengths octets including the terminating zero length octet)
is limited to 255 octets.
Roger