[mwpmaybe]

The solution to this is SRS[0], but yes, not every mail-forwarder implements this (correctly), and it seems to break DKIM. The good news is that an SPF soft-fail and a DKIM pass usually means a DMARC pass. More information here[1].

0. http://www.openspf.org/SRS

1. https://blog.fastmail.com/2016/12/24/spf-dkim-dmarc/

[jlgaddis]

Even with SRS, the "reputation" of the "middleman" (from Google's perspective) still suffers.