Having trouble viewing all your IMAP folders on iPhone? (For better or worse, I’m a GTD-style reference filer when it comes to archived messages.)

Settings > Mail > [account] > Advanced > Imap Path Prefix

Set it to “INBOX” (rather than just “/” or “/INBOX”).

I use Webmail.us as my mail provider, so your results my vary by who hosts your mail and what software they are using.

(thanks to Matt Devost).