Without knowing your setup, here are some reasons why email can disappear. If you have an IMAP-account: * Your server-quota is reached and the server deletes them. * Your settings for disk space in ''account settings /sync&storage'' or in ''property / quota'' on your folder. * Someone (you?) deletes them on server from another device or webmail and your pc-inbox was then syncronized. Remember that '''not''' compacted folders still has all deleted mail inside that will take up space. * If you want to keep your mail, move (or copy) them to a local folder, * Regularly compact your folders (esp INBOX) and empty your trash. * If you need to safe addresses set up a filter that add all new addresses to a new address book. I would also recommend that you set your virus-protection '''not''' to scan your profile. Because a folder is a single file and if there is a suspicious attachment to one of your mails, your virus-protection will wipe out the file with '''all''' messages in it