Sun email leak?

An email address I've only used at Sun (sunsolve, download) and OpenSolaris for registration (no email ever sent from that address) is receiving spam from a Unix shell provider (which means it's not untargetted).

Fortunately they're so incompetent they don't have working rDNS, so it's blocked by my antispam ruleset.

But this sounds like I can't trust one (or both?) of sun.com or opensolaris.org; I'm thinking the latter :-(