Most mailing lists now implement the Sender Rewriting Scheme to ensure compatibility with SPF and DMARC etc.

However, not all do. If a mailing list forwards e-mail from a domain with an SPF record without rewriting the sender, then the e-mail whilst legitimate will fail the SPF checks.

I've already submitted a proposal to implement moving the e-mail to the Axigen quarantine if it fails SPF rather than reject it outright. In this way e-mails from legitimate maillists which aren't compatible with SPF can be detected. However, in order to allow receipt of e-mails it would also be necessary to implement a white list of e-mail hosts - e-mails received from an ip address on this white list would not be subjected to SPF checks.