Looking for ways to increase the amount of revenue it gets from subscriptions and reduce its exposure to the volatile advertising market, Yahoo! Inc yesterday started to offer a paid-for version of its previously free web-based email service. Yahoo! Mail Plus has been priced at $29.95 per year. Users get 25MB of storage, the ability to send up to 10 attachments of up to 10MB total, POP access, hard-drive archiving and extra filters.