Evolution creates a folder in your home directory called simply "~/.evolution". The "." makes it hidden from normal viewing with ls or file browsers like konquerer. The directory tree looks like this:
/home/gruemaster/.evolution
|-- addressbook
| |-- local
| | |-- razman.gruemaster.com
| | | |-- addressbook.db
| | | `-- addressbook.db.summary
| | `-- system
| `-- views
|-- cache
| |-- http
| | |-- 00
| | |-- 01
| | |-- 02
| | `-- 03
| `-- tmp
| `-- evolution-tmp-4vK1c6
|-- calendar
| |-- config
| |-- local
| | `-- system
| `-- views
|-- mail
| |-- config
| |-- local
| | |-- Drafts
| | |-- Drafts.cmeta
| | |-- Drafts.ev-summary
| | |-- Drafts.ibex.index
| | |-- Drafts.ibex.index.data
| | |-- Inbox
| | |-- Inbox.cmeta
| | |-- Inbox.ev-summary
| | |-- Inbox.ibex.index
| | |-- Inbox.ibex.index.data
| | |-- Linux Questions
| | |-- Linux Questions.cmeta
| | |-- Linux Questions.ev-summary
| | |-- Linux Questions.ibex.index
| | |-- Linux Questions.ibex.index.data
| | |-- Mandriva
| | |-- Mandriva.cmeta
| | |-- Mandriva.ev-summary
| | |-- Mandriva.ibex.index
| | |-- Mandriva.ibex.index.data
| | |-- Outbox
| | |-- Outbox.cmeta
| | |-- Outbox.ev-summary
| | |-- Outbox.ibex.index
| | |-- Outbox.ibex.index.data
| | |-- Sent
| | |-- Sent.cmeta
| | |-- Sent.ev-summary
| | |-- Sent.ibex.index
| | |-- Sent.ibex.index.data
| | |-- winex
| | |-- winex.cmeta
| | |-- winex.ev-summary
| | |-- winex.ibex.index
| | |-- winex.ibex.index.data
| | |-- woodworking
| | |-- woodworking.cmeta
| | |-- woodworking.ev-summary
| | |-- woodworking.ibex.index
| | |-- woodworking.ibex.index.data
| | `-- woodworking.sbd
| | |-- requests
| | |-- requests.cmeta
| | |-- requests.ev-summary
| | |-- requests.ibex.index
| | `-- requests.ibex.index.data
| |-- pop
| | |--
gruemaster@pop.gmail.com
| | | `-- cache
| | | |-- 00
| | | `-- 01
| |-- vfolder
| | `-- Mail from mothergrue.cmeta
| `-- views
|-- signatures
`-- tasks
|-- config
|-- local
| `-- system
`-- views
Mail is stored in .evolution/mail/local in mbox file format (plain text with mime and other format encodings for attachments). Sub folders in your local mail area have the .sbd extension. Indexes and other metadata is stored in the <Folder>.cmeta or <Folder>.index & <Folder>.index.data files. Notice that vfolders are just another cmeta file, essencially an index to each piece of mail that matches a query defined in the vfolder properties.
Hope this helps a little.
