The SPF specification limits the number of DNS lookups to 10. If your SPF record results to more than 10 DNS lookups then SPF will fail and result in SPF PermError: Too Many DNS Lookups. The SPF mechanisms counted towards DNS lookups are: a, ptr, mx, include, redirect and exists.
The mechanisms which do not count towards the limit are "ip4", "ip6" and "all".
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