Nokia E5 Phone memory full!

Memory in use: 254 MB
free memory: 5.1 MB
Calendar: 13 KB
Contacts: 38 KB
messages: 10 MB (deleted all attachments by the way)
Images: 0 B
sound files: 0B
video clips: 0 B
documents: 32 KB
MIDP apps: 1 MB
SIS apps: 16 MB
Other files: 226 MB 

I had exactly the same problem. I have no idea what the "other files" were, but doing a soft reset (where you won't lose contact and calendar info) reduced them from around 240MB to 70MB (which increased to 90MB when I updated the email app. I followed the instructions below for a soft reset and haven't tried a hard reset but included below in case it is helpful to anyone:

To hard reset your you just have to press *#7370# and press Dial. The phone will request the security code that is by default 12345. Please be aware that you will loose all the data in your phone, so you should backup all relevant information.

If you want to soft reset your you need to press *#7780# and then Dial. The security code is 12345. Once you complete this, your phone will come back to factory settings, but you will not loose personal data. Anyway it is recommended to make a backup before performing any of the mentioned procedures.

You need to close all open apps (press and hold the "home" key and close everything other than "menu" and "standby"), and put the phone in offline mode (red phone key, then select "offline - 3rd option from bottom of list).

I suspect I'll get this problem again but as long as this keeps working it is manageable. Really annoying though - took me ages to find a fix that worked.