the current SPF sets customers up for failure, the RFC dictates you can only have 10 DNS looks up...Zuora alone has 5 at the root, 3 sub includes via _spf.google.com, total of 8... https://tools.ietf.org/html/rfc7208 (4.6.4) this requires the customer to leverage a 3rd party SMTP relay similar to mailjet or sendgrid...we were forced to leverage a 3rd party due to the size of the SPF and the impact to normal day to day mail delivery...once you cross the 10 includes limit, its hit or miss if it will work depending on how strict the antispam software is with SPF and the RFC rules
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