SPF optimiser causes check/print-ir to depend on DNS

[ad8-bdl]

(a sibling problem to #1071, I believe)

check / print-ir should not depend on external things such as DNS.

Using the SPF Optimizer causes the check / print-ir commands to execute DNS lookups which in and of itself is not great; worse is that failed DNS lookups raise incorrect validation errors.

For example, where the current SPF record for the domain includes an invalid name mailsenders.netsuite.com but the config file is otherwise valid:

% dnscontrol preview --expect-no-changes
2021/12/24 07:27:33 printIR.go:88: 2 Validation errors:
2021/12/24 07:27:33 printIR.go:94: ERROR: in included SPF: lookup mailsenders.netsuite.com on 192.168.65.5:53: read udp 172.17.0.2:38283->192.168.65.5:53: i/o timeout
2021/12/24 07:27:33 printIR.go:91: WARNING: problem resolving SPF record: lookup mailsenders.netsuite.com on 192.168.65.5:53: read udp 172.17.0.2:38283->192.168.65.5:53: i/o timeout
exiting due to validation errors

[tlimoncelli]

Good point that check / print-ir should not depend on DNS.

The spf optimizer uses DNS but fails quickly to using spfcache.json if DNS is down. Maybe for check/print-ir it should just use the file.

[tlimoncelli]

Sadly SPF is in maintenance mode. I'm not going to be adding new features.

Closing. Feel free to re-open if it becomes hot again.