I suspect the parent poster is talking about spam sent from gmail to non-gmail accounts - such as my own self-hosted mail-server.

I receive 5-20 spam messages a day from @gmail addresses. Not a huge number, but some days it jumps to 50-100. (These messages really did get routed through google, rather than being faked.)

Spam from gmail's smtp servers. There are a number of spam services oriented towards small business. Their users are required to use their own gmail credentials. MailShake and FunnelBake are two services from my inbox this week, though they're deliberately hard to identify - no note in the headers, no footer on the email, customers encouraged to set up domains aliasing "unsubscribe" links, etc.

This is a growing source of spam for me personally and services I've worked on that have public email addresses (eg. support@), especially if near a mailing address. (Other services scrap lists of "local" businesses and sell them to the end users of the spam services.) Blocking gmail smtp is a non-starter due to popularity, graylisting doesn't help, and I haven't been able to find anywhere they take spam reports; search results are overwhelmed by discussion of reporting spam as a user of GMail.