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Issue
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IPv4 addresses
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IPv6 addresses
The 'ptr' mechanism shouldn't be used because it's slow, resource intensive, and not very reliable.
Terms
mx
pass
if the sender's IP address is in the A or AAAA record of this domain.
or else
PTR checks should no longer be used. See
RFC 7208, section 5.5
.
or else
?all
Don't state if this IP is allowed to send this email.
Included records
v=spf1 mx ptr ?all
The 'ptr' mechanism shouldn't be used because it's slow, resource intensive, and not very reliable