Gmail URL Parameters

It turns out that when using multiple sign-in, the first account that one signs into is forevermore the "default account" for that browser session. This applies to all Google Apps features: not just logins to https://mail.google.com/, but also things like OpenID sign-ins.

The solution was simply to sign out, log into the gmail.com account first, and then log into the Google Apps accounts.

This is a known issue with all of Google's services. They do not support the .eml or the less common .mht, both of which are known and established formats. In this case it has been (for years now) one area that all the others (Microsoft, Apple, Mozilla, and most of the rest of the community) are ahead of Google on. The only option, aside from convincing Google to support it, appears to be to either bear with the extra info and read it as a raw text file or to save it and open it with almost any other email client, such as Thunderbird or Outlook.