After using offlineimap a lot to backup my mailac­counts with­out hav­ing the mail acces­si­ble in KMail I’ve man­aged to see the backup in KMail
KDE ver­sion is KDE4.x, offlineimap is 6.1.2, Disto is Arch­Linux and this is what I’ve done:
Setup of .offlineimaprc:

[gen­eral]
meta­data = ~/.offlineimap
accounts = martin

[Account mar­tin]
local­repos­i­tory = martin_local
remoterepos­i­tory = martin_remote

[Repos­i­tory martin_local]
type = Maildir
local­fold­ers = ~/Dokumente/MailBackup/MartinAtSchmart
sep = /

[Repos­i­tory martin_remote]
type = IMAP
remote­host =
remo­teuser =
remotepass =
max­con­nec­tions = 1

Run offlineimap.
Then:

  1. Cre­ate a folder named “Backup” in KMail/Local Folders
  2. go to ~/.kde4/share/apps/kmail/mail and cre­ate a sym­link to ~/Dokumente/MailBackup/MartinAtSchmart with the name .Backup.directory
  3. Restart KMail

Now the mails should be acces­si­ble via the “Backup”-folder. If not try to rebuild the index (right-click on the folder name).