What's your strategy for archiving emails in Mail.app? Do you archive your Sent & Trashed emails too?
I use Mail app's "smart mailboxes" instead of copying and moving the actual messages in Mail. For example, to archive July 2011:
- create a new smart mailbox,
- name it "Mail Archive July 2011" or whatever,
- set the find criteria to "Date Received is in the date range 1 Jul 2011 to 31 Jul 2011",
- you will probably want to check the "Include messages from Sent"
- Hit okay and in a moment you have a folder contain all of July's email
- Right-click the smart mailbox and choose the "Archive" option and save.
After this you have the option of keeping the smart folder or deleting it. Spotlight (in OS 10.6.8) searches the .mbox archives Mail produces, so your archive remains searchable.
I've recommended MailSteward to several clients. It maintains a separate SQLite (or MySQL in the "pro" version) database of archived messages. It handles de-duping too. Messages are searchable, attachments are stored and you can reply to archived messages. (Reply will open in Mail.)
Basically, I always BCC to myself, so never archive the Sent folder.
Since you're in OS X Lion, the best way to "Archive" a message is perhaps using the integrated (new) way to Archive: ⌘Y
There are many options, but I recommend the module archiving emails OpenKM. Because allows us to use the repository as a document management system to store messages massively. The mail file is an automated process for the preservation and protection of all emails.