Hello,
I am using kmail2 for 2 email accounts (imap) with no problems so far.

Today I noticed that I cannot view some of my old sent emails that are stored in local kmail folders. The emails are listed normally (subject, size, etc) but when I open it the body is empty. I suspect that maybe something happened after migration to kmail2. But I am not sure.

Any thoughts?

I don't really know the real problem and I'm no expert either, but I've had this before and generally, what has helped me was to switch to a new backend server for Akonadi.

If you are unwilling to do so or don't mind losing some data (not the actual emails or folder structure, but things like read status information or tags), you could also keep the backend and start a new database, but that might not always help.

What do you mean "switch to a new backend server for Akonadi"? I am not sure what I have to do.

Akonadi relies on a database backend to store all your data. This is really all I myself am able to tell you about that. I have no idea how it works. But it is fairly easy to switch. Most distros I think use MySQL or SQLite. These should be the 2 options you have, I think MySQL is recommended, but neither is completely bug-free. There is also PostGreSQL which isn't officially supported yet but has never given me this problem, unlike the other two.

What you do is you use krunner or the Kmenu to find the Akonadi configuration tool. In one of the 2 tabs you can pick from a drop down menu which backend you want to use. I don't think you'll have to do anything else, just restart the server (you can do this in the same tab). If that doesn't work, try a system restart.

Maybe somebody more competent than I can actually explain you why this happens or if there's a better option than switching the database server. I am really just a normal user who was having problems (still do) with a beta quality product and fiddled and googled until I happened over something that worked.

But it might be easier for you to first back up the directory $HOME/.local/akonadi, and maybe a few files in .config/share/akonadi and .kde4/share/config (you'll have to see if anything backend-specific is in there, but I don't think so), and see if a clean database won't work for you.

Sorry this all comes from memory. You'll find more details in this forum if you can't figure it out, or just ask again here.

As to your original question: judging by the symptoms, it is akonadi that doesn't work. Your emails should be just fine.