My eM Client deletes any message older than a year from my local folders. How do I tell eM Client not to remove any messages from local folders?
eM Client will not delete messages from Local Folders unless you instruct it to by clicking on the message and using delete. The most likely cause is that your account is configured as IMAP, and the messages are being deleted or moved from the IMAP folders (not local folders) by either the server or another device connected to the same account.
If you have Automatic Archiving enabled, it may be configured to move messages to the Archive folders after a certain time, but you would have had to have set that up yourself. It is not enabled by default. The configuration is in Menu > Tools > Settings > Mail > Automatic Archiving.
Rules can move messages elsewhere or delete them, but only affect messages as they arrive, so would not move or delete older emails unless you ran the Rule manually.