FYI:
SMTP transitioned from A to MX.
No, it didn't. A surprising number of real mail hosts only publish an A, and I lost the battle to say that MX shouldn't fall back to AAAA. It does.
SPF could have been the same except people were impatient and had unrealistic expectations of how long it would take.
Perhaps it's a generational thing. I'm not very interested in transitions that won't happen until after I'm dead.
R's, John
