Posted by David Besbris, Engineering Director Update (2:37 pm) : We've fixed the issue, and Gmail should be back up and running as usual.
Posted by Emmanuel Pellereau, Software Engineer Quite a few of you use Gmail's custom "From:" to send messages with one of your other email addresses listed in place of your Gmail address. Since these messages are sent by Gmail's servers but "from" a non-Gmail address, we have to include your original Gmail username in the "Sender" field of the message header to comply with mail delivery protocols and help prevent your mail from being marked as spam
Posted by Keith Coleman, Gmail Product Director We get asked all the time why Google keeps its products in beta for so long. And Gmail, five years after launch, is consistently a subject of this questioning, even of jokes