While debugging a SPF record I found spf-record.de Show archive.org snapshot to be very helpful.

• it lists all IPs that are covered by the SPF record
• shows syntax errors
• helps you debugging errors like DNS lookup limit reached
• it also lets you test a new SPF strings before applying it. This can save you time as you don't have to loop with operations

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Also the advanced check at vamsoft.com Show archive.org snapshot has a very good interface to test new SPF policies.