automatic deletion of mail
How do I stop mail from being automatically deleted after a period of time?
This is not a browser-related issue, but I think I can help you anyway. What mail service are you using? (the website/program you use to display your inbox, or the second half of your email address - after the '@')
Usually, you will need to check auto-deletion settings and/or expand mailbox storage. How to do that depends on your mail service, so reply which one you use.