Mail - external mailbox via symlink

Hi All,

I have my email archive going bigger, but i want to keep it accessible trough mail, so no export...

I have tried to copy the mailboxes in /Library/Mail manually on another drive and put a symlink at their place.

It works great for reading. it seems the same and also the search works fine.

The problem is that if I try to add an email it denies it telling me that the mailbox is read only.

I have tried to check permission and rebuild the mailbox but nothing. do you have something to suggest?