An included record carries an exp= modifier
MINORWhat it means
example.net publishes exp=, and the standard says an included record's explanation is never used. It is ignored, so the explanation you expect senders to see is not the one they get.
How to fix it
Nothing to fix on your side. Publish exp= on your own record if you want a custom explanation, or ask example.net to drop it.
Check your own domain
This page describes the condition. To find out whether your domain has it, run the SPF test or the full checkup, which examines every record at once.
Understand it properly
This page covers one condition. For the whole picture, What is SPF, and the ten-lookup limit, or start at the Health Library.
Where this comes from
We judge this against RFC 7208 section 6.2. Every finding on this site cites the specification behind it so you can check the work rather than take our word for it.
Other SPF conditions
SPF_EXP_IN_INCLUDE
Every fix on this site is yours to implement. If you would rather someone did it, I take this work directly.