Why do I get a 'connection to the outgoing server "smtp.gmail.com" failed' message in iOS Mail?

Today I noticed I have 3 emails stuck in my Outbox, and when I try to re-send one, I see: If I press **Settings**, then select "SMTP Gmail SMTP Server", and "Gmail SMTP Server" (under PRIMARY SERVER--it is the only one shown as "On"), I see: I can't edit anything here. Has Gmail changed the way their SMTP authentication works? How do I fix this?