I've lost all email in inbox back to 3/30/13 (currently 4/11/13). HELP?!?

[Kevin W]

The question pretty much says it all... After days of "unexpected error" messages in my browser, this morning I lost all messages in my inbox after March 30, 2013. They weren't moved accidentally or deleted. They are gone. I have sent in a feedback message, and sent contact on Twitter. But am also wondering if anyone else has had a large deletion of email or any contact with the Yahoo! help team.
Thanks.
Edit: I've already received one answer about backing up via an email client. Thanks for input, but that's not helpful for this particular issue. It unfortunately wasn't done with these emails, but I'm all set up for POP access with my Premium account.
The most helpful responses would be specific ones relating to having all emails deleted that were dated after 3/30/13. Thanks again.