Ah, I can read *new* messages that come in, not any of my old messages.  There's a clue - I just don't know what that means.

Try and start akonadiconsole, choose your account (agent) and select "Synchronize All"

I'm not seeing any change.  Mail that I already had (prior to migrating from kmail in kde 4.4 to kmail in kde 4.7) still doesn't want to show up.

My IMAP account (GMail) does work fine whether it's new email or old email.  Locally-stored old email is not displaying.

We are at 4.10 and I assume this is no longer a valid problem for the reporter (given the age of the report), and I do not have this problem here with 4.10 (and a lot of old mails)

Unfortunately, no, even with KDE 4.10.0, it still does NOT work for me.  Just going back to July 2007, for example, I can't read any of the emails, even though they show up in the index just fine.  I'm assuming, then, that these emails will simply be lost to me forever.

Thanks for your feedback, reopening then.
If I understand you correctly, then you see the header of the mail (e.g. in the message list the subject, date, sender, etc.) but you see no message content, right ?
What you could do is to grep for such a subject text in your local maildir folders and find the file which contains the message. Then look inside the file and tell us if the message body is also missing from the file itself, please.

$ grep -A 1 'Contact Information Update' ~/Mail/inbox
Subject: Contact Information Update
Date: Fri, 20 Jul 2007 17:07:00 -0400

And if I look in that file with "less", I see the email headers start on line 1301711 and end on 1301755, and the email contents (multi-part MIME message) starts on 1301757 (with the blank line in between, as expected), and goes to 1302164 (darned Member of Parliament with mixed text/html messages).  While the html is hard to read, the mime-encoded plain text seems to be fine.

I'm wondering if kmail decided to switch formats - because this inbox's last message is:

Date: Thu, 28 Jul 2011 02:15:02 -0600 (MDT)

whereas my real inbox in kmail has plenty of messages since that date.  Those seem to be in ~/.local/share/akonadi/file_db_data...

I think what you're missing is a resource which loads your old inbox mbox file.
What you find under ~/.local/share/akonadi/file_db_data... is just a _cache_ of the new mails (or part of the mails) not the mails themselves.

Please check your kmail settings under Accounts -> Receiving.
You should have (or add a new one) of type mbox which points to the old mbox file - then you should be able to see all your old mails.

To find your new mails (the ones you received from July 2011 on) should be somewhere else. Check your receiving accounts settings.

Ok, I've created that mbox... unfortunately, that means they're all going into a different folder, so the header info still shows up in my "KMail Folders / Inbox" but the header AND message shows up in a whole separate location :(  Maybe filtering would help, but that doesn't work anymore, either :(

Intresting ... If you did not have the mbox resource before, I wonder from where akonadi got the header info then ...

You probably should discard the akonadi database and start from scratch

This bug has only been reported for versions before 4.14, which have been unsupported for at least two years now. Can anyone tell if this bug still present?

If noone confirms this bug for a Framework-based version of kmail2 (version 5.0 or later, as part of KDE Applications 15.12 or later), it gets closed in about three months.

Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.