I'm not aware of any email service what would allow you to tag some incoming messages with an "expire in 30 days" or something rule. Except the spam folder. Bu

I'm not aware of any email service what would allow you to tag some incoming messages with an "expire in 30 days" or something rule. Except the spam folder. But again, the main purpose of Gmail is to harvest your behaviour data, not providing you a good email service.