SPF Record -all blocks autofrwarded emails

I had my SPF set as v=spf1 a mx -all, which works fine.

However, one of my clients has said that they are not receiving auto forwarding emails from their personal web address.

Looking into this, I set up an auto forward from my personal virginmedia email address, to the domain name of my server and that too got blocked. I am assuming that because there is an email coming from an email address hosted off my server, but being routed through virginmedia, the -all is blocking it.

Changing to ~all allows autoforwarded email through, but this defeats the object of having an spf.

Any ideas pls?

Thanks