This summer Apple changed built-in mail app to support "archive" button (at least for GMail and GApps-based accounts), but I have found that I need to delete emails much more often than archive them. Right now the only way to delete them that I know is moving messages into Trash folder, which is quite cumbersome. Is there a way to bring back "delete" instead of "archive" button or any other way to quickly delete messages?
Simply go to Settings -> Mail, Contacts, Calendars -> Your Gmail Account and turn "Archive Messages" to "Off".
Ok, for iPad users. I just literally solved this. I spent around an hour (I know) going through various forums and posts until.
Go to settings> Mail,contacts,calendars > account> advanced> and change the check box from archived messages to delete.
You also have some options for changing the folder paths here, but don't worry about it. Save the changes and click done. And next time you swipe away a message it would have a red box with trash instead of archive. You are welcome.
One way to do this is to setup gmail using IMAP-setup instead of the normal Gmail-setup. That way you can configure if you want the messages to be archived or deleted when you push the trash-icon.
You can find Gmail IMAP settings instructions here: http://www.youtube.com/watch?v=uQ22euWXYog