I have been grateful for my 10+-year mail archive many times.
On the other hand, there's mail archive rot too:
I lost most of my mail archive around 15 years ago when a migration from my Lotus Notes university account to several IMAP accounts went terribly wrong. And many mails lost their metadata and/or attachments during later migrations. All in all, however, my mail archive has remained very useful.
There is only one major issue:
I use Apple Mail due to its integration with my private CRM software and with Apple Mail, you have to keep your mail archive in sync even if you use IMAP. That means a few 10 GBs on each Mac I use - expensive storage in the age of SSDs! Even worse, if you are on the road, you pay an addition toll for expensive mobile data or (usually) slow data in public wifi networks etc. Backup becomes more expensive due etc.
Instead of risking all that data why not pay for a Google Apps account under a domain you control and make a backup using MigrationWiz.com to Google? Then delete all the old mail from Apple Mail and start clean. You can use MigrationWiz once a year to keep backing up your data.
On the other hand, there's mail archive rot too:
I lost most of my mail archive around 15 years ago when a migration from my Lotus Notes university account to several IMAP accounts went terribly wrong. And many mails lost their metadata and/or attachments during later migrations. All in all, however, my mail archive has remained very useful.
There is only one major issue:
I use Apple Mail due to its integration with my private CRM software and with Apple Mail, you have to keep your mail archive in sync even if you use IMAP. That means a few 10 GBs on each Mac I use - expensive storage in the age of SSDs! Even worse, if you are on the road, you pay an addition toll for expensive mobile data or (usually) slow data in public wifi networks etc. Backup becomes more expensive due etc.