Does your SPF record length have a limit? Long answer short, yes. Your SPF record limit is a 255 character string limit exceeding which can break SPF and lead to authentication failure. If you have been coming across the message “SPF exceeds maximum character limit”, that simply implies that the SPF record in your DNS is longer than the RFC-specified (RFC 7208) string character limit. This can be a problem especially if the delivery of your emails is heavily dependent on SPF alignment.

Already have an SPF record? Check its validity with our free SPF checker.

Optimizing SPF to stay under the SPF length limit

1. Avoid using the ptr mechanism in your record. This is because it isn’t currently supported according to RFC guidelines for SPF and further increases the number of characters in your SPF string
2. If you want to bypass the 255 character limit for SPF to get around the error message without failing SPF, RFC permits the usage of multiple strings for a single SPF DNS record. However, these strings should all be connected together without any space in between for your record to be valid. Make sure it’s one continuous line and not broken up into multiple lines, as each line is treated as a separate record. Multiple records for a single domain will break SPF.
3. Make sure you remove redundant, repeated, and NULL mechanisms within your SPF record which also adds to the character limit. This ensures that your record is short, crisp, and valid.
4. You can use our SPF flattening tool to optimize your record automatically that never exceeds the 255 character SPF record length limit

What happens when you exceed the SPF string character limit?

If you exceed the 255 character limit for SPF, your emails will fail authentication on the receiver’s side as the record in your DNS will now be considered invalid. Depending on your policy and alignment mode, your emails may get lost in transit and never get delivered to your recipients. It is recommended that you configure a DMARC report analyzer for your domain to get reports on failed SPF authentication. With reporting enabled in these scenarios you will receive an error message along the lines of “SPF exceeds maximum character limit” or your DNS will communicate with BIND to display the message: “invalid rdata format: ran out of space”. Either of these simply implies that you have exceeded the SPF record limit. 

Restricting your SPF record limit with PowerSPF

PowerSPF is your one-stop solution for all SPF-related problems. Whether it is staying under the lookup limit of 10, or restricting your record length to the specified limit, PowerSPF does it all instantly and easily!

Optimizing your DNS records to enjoy error-free implementation is a possibility with PowerDMARC’s email security suite. Sign up for a DMARC trial to enjoy a one-click optimized SPF that never exceeds the SPF 255 character limit

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Yunes Tarada

Domain & Email Security Expert at PowerDMARC

Yunes is an Operations Team Lead at PowerDMARC with expert knowledge in email authentication and security. Yunes is a Microsoft-certified Azure Administrator Associate with certifications in CompTIA A+ and many more.

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