I reviewed Mail Steward ($49.95) before for Surfbits and thoroughly enjoyed it, so I was happy to take a look at the latest version, especially as I use it every month as part of my monthly back up routine.
As you can see from their site they have a number of features:
* Works seamlessly with the Mac OS X Apple Mail app to archive all your email in a relational database.
* Will import most mbox files exported from Microsoft Entourage, Eudora, and other email clients.
* Works with all locally-stored POP, .Mac, and IMAP email accounts in the OS X Mail app.
* Select email from archive by date range and keywords in the To, From, Subject, Mailbox, or Body fields.
* Sort by date, To, From, Subject, Mailbox, or unique ID.
* Add your own tags to email & import MailTags©
* Search binary attachments that contain any text.
* Print email list, or individual email, or all email in a list.
* Save email list, or individual email, or all retrieved email to a text file.
* Reply to individual emails.
* Export emails to a tab-delimited text file, a separate database file, an mbox file, or an SQL file.
* Merge database files together.
* All email folders are left undisturbed.
* Options to store attachments, HTML, enriched text, and raw source, as well as plain text.
* Universal binary runs on PowerPC and Intel Macs.
* Native Cocoa application that supports OS X 10.4 (Tiger) and greater.
So, it is MUCH more than a backup application! I particularly liked the new feature that allowed you to search attachments. I am not alone in appreciating this application.