Consider staying below 10 FQDN lookups within a SPF record. If you go above this, most SPF checks will show errors (even if they still work).

You can include IP addresses once you have gone above the 10 FQDN limit. However, remember that these entries will be static and, like most static IP addresses, might change without warning.

If your SPF record is above 225 characters, you may run into issues with NIOS refusing to save the record.