iPhone smtp issue - won't send mail

http://discussions.apple.com/thread.jspa?messageID=8709794

My manual gmail smtp settings had been working fine. All of a sudden I couldn't send mail. The error was: "Cannot send mail. The sender address was invalid."

The apple forum url above contains a buch of possible fixes and workarounds. The one that worked for me was to explicitely add username and password to the gmail smtp server settings. I don't know if it was using defaults before and that broke, or if the username/pass was in there and got lost.