One day, all of a sudden all of my sent emails disappeared from my sent email folder. Now they disappear usually at the end of each day. How can I get my sent emails back? Or, are they lost forever?
If your settings were unexpectedly changed that's a sign that you account has been hacked. I recommend changing your password, turning on 2-step login verification, and checking your other acocunt information including email forwarding, message filters, etc to make sure a backdoor wasn't left in place to help the spammer hack your account again: