If you encounter this message, it means your SPF record contains a mx mechanism which has one or more Mail Exchange (MX) resource records that contain more than 10 address records - either "A" or "AAAA" resource records. Email sent from this domain will have email delivery problems due to the permerror that will occur due to this error. From RFC 7208 section 4.6.4: The evaluation of each “MX” record MUST NOT result in querying more than 10 address records—either “A” or “AAAA” resource records. If this limit is exceeded, the “mx” mechanism MUST produce a “permerror” result.
To illustrate where this error can occur, please look at the below with particular focus on the mx which means the recipient server should perform a MX Record lookup for that domain to get a list of MX records. Now if any one of those MX records contains > 10 A or AAAA records this error will occur.
v=spf1 mx ip4:1.2.3.4 ~all
When the MX lookup is performed against the domain, it will return a list of MX records. If one of those MX records has 10 combined A & AAAA records the error will be thrown.
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