GMail allows users to send through GMail as another address, provided that they've registered that other address as either an alias, or a non-alias that they control. My editor address has been registered as the latter. I have sent to the list using it via the GMail SMTP servers; I'm trying it now through the GMail webmail, I have no idea whether the webmail adds the requisite In-Reply-To header to prevent thread breakage; if there's anyone that routinely responds to list posts using GMail's webmail, please chime in, as that will be confirmation that it does.