How do I stop Apple Mail from auto-deleting my emails?

Yea, this is crazy. I do not use any device to check email except a laptop and a desk top. But, neither device has any rule or alter regarding read email. Yet, every read email on my desk top is moved to trash folder after a certain number of days - perhaps after 7 days. This all started when I downloaded OS X. I receive a lot of email per day, so when email goes to trash, I may not find it again. I have an IMAP account for email. But, there is not box to check or uncheck that direst email to be deleted after it is retrieved. But, my problem is not deletion. My problem is the email being moved to the trash folder automatically.

Here are some possible reasons why this might happen.

1. Junk filtering, or a Mail rule that you created, is deleting the messages.

2. Mail is being deleted on another device that synchronizes with the same IMAP or Exchange account. The account may be accessed using both the IMAP and POP protocols, which could happen with some mail servers. POP access could cause mail to be deleted from the inbox. Make sure that no other mail client is set up to access the account with POP.

3. Someone else has access to the account and is deleting messages.

4. Mail is being redirected or filtered on the server. For instance, there are settings in the Mail web application on icloud.com to forward incoming mail and delete it after forwarding. If you've ruled out #1 and you have control over such behavior on the server, disable it and see whether there's a change.

5. Some mail servers have a setting to delete mail automatically under certain conditions. You would access that setting through the server's web interface, not through Mail.

6. In the settings for the IMAP account in Mail, the field labeled IMAP Path Prefix in the Advanced tab should be left blank unless a server administrator tells you otherwise.

7. You installed a third-party "plugin," such as "MailButler," that changes the behavior of Mail. Remove the plugin(s) according to the developers' instructions and test. If testing shows that a plugin is causing the problem, but you still want to use it, refer to its developer for support or an update.

Does it delete all of them at once, or is it deleting everything older than 1 day, 1 week, or 1 month? Are we talking about the Trash folder, or any mailbox?

Verify the settings are correct in Mail preferences for each account. You need to do the same for all devices such as the iPhone also.

If you delete a message, does it normally go to the Trash mailbox? Can you confirm that?

Which mailboxes do the messages disappear from?

Do you have more than one account? If so, is this happening with one account, or all? Are the accounts (or account) IMAP or POP?

Have you gone to the webmail site and verify that the messages are missing there also?

I was searching for some help regarding the same issue: mail is being automatically deleted from my inbox. It's happening about once or twice daily the past few days. The mail goes to my trash folder so I can at least retrieve what I need and move it to another folder where it it stays until I delete it myself. It's a IMAP account. I checked my junk mail filtering and any rules that could have been set up do make this happen but all looks fine. I made no changes so I'm at a loss as to why this is occurring. I use only a mac account. Any ideas?