Just went to login to my Yahoo account and I can confirm that yes, they do. Everything is deleted if you don't login for four months.

Just happened to me too. There is no better way to piss off your uses than deleting all their email. I could see having a 2 year deactivation, but 4 months? I'm sure the storage space isn't an issue, so this can only be a ploy to try to force users to log in.

Marissa Mayer has her work cut out for her. This, along with probably 10,000 other things, needs to change if Yahoo wants to compete with Google (and Microsoft?).

I have had a different experience - I have gone longer than 4 months between logging in and have not lost everything. Unless of course I have some box/account/app somewhere out there logging in unbeknownst to me :)

That must be the case. You should check account settings to see whether you have permitted such apps or sth rogue.

As it clearly says it does so and I confirm as my inbox is wiped clean too. There were just few "Welcome to xyzabc.com" mails.

This sucked and was the reason i stopped using them. I dont care enough to try them again now, purely because I lost mail this way

I log in to my Yahoo account about once a year to reset a password on <insert ancient web service account>, and I've never experienced this.