Current RFC proposal has nothing about maximum SPF record length.
I'm unaware if it 65000 (TXT DNS limit), 1400 or 512.
Without activating EDSNO to negotiate longer UDP packets (and many DNS
servers do not support EDNSO), max DNS total packet size is 512
bytes. Above that, the querier gets a TC bit in the truncated response
packet, and should re-submit the query over TCP, at which point tons of
firewalls will block the TCP connection to port 53.
SPF will look pretty stupid and self-aborting if it can't come up with a
way to stay within 512 bytes.
Len
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