Mail is being deleted automatically

How is that account set up on your mac? IMAP or POP?

I can see a situation where mail would be deleted after one month: if it is a POP account, there is a setting for what to do with messages after they are downloaded:

As per this article : Mail for Mac: Mailbox Behaviors preferences in Mail

Trash Mailbox : Note: If you select None, deleted messages may temporarily remain in a mailbox, but are hidden or dimmed. To show or hide these messages, choose View > Show Deleted Messages or View > Hide Deleted Messages.

Mail erases deleted messages at the specified time. Select a setting other than Never to avoid exceeding storage limits set by your email account provider.

Erase deleted messages :

If you selected None for Trash Mailbox, you can choose to have Mail permanently delete messages automatically.

If your email account provider sets up the server to delete older messages, the messages are deleted regardless of how you set this option.

There are settings on an iPhone to set time limits for trash removal. You have to go to Mail settings and click on the account till you get to the advanced settings. Check all devices for this setting.

Another point is why would you want to use the trash for storage. Point is what's happening is just what is most likely to happen at some point or other either by accident or with a setting change. If you truly never want to delete messages, move them to other mail folders for organization and storage, or use Archive to store them. Trash should be used only what it is intended for----Trash.....

Most mail providers have a time limit on their trash or settings for it. Not sure about your provider, but they change from time to time. I had that happen to me where they randomly delete messages in the trash.

Trash is just another folder. But it's intended use is for messages you no longer want. As you see on the Mac, it has settings for removal. An update may change the settings or corruption could happen and settings could change. I've seen that happen several times.

If you want to save messages, then move them to another folder or archive them. What's so hard about that? If you feel the need to use Trash as a storage folder, then expect this to happen from time to time.

As for your Android, I don't know it does. But surely there must be settings for trash removal.

Gmail deletes files in the trash or spam folders after 30 days.

That has nothing to do with any mail client, on any platform.

I expect that other mail providers may work similarly.

Now if you have mail that is in some "regular" folder in your provider's server, it should not be deleted. But there is no evidence to suggest that Mail is somehow involved.

Just to make sure: do the messages simultaneously disappear from the server, your mac and your phone?

Did you perhaps move such messages accidentally to a folder under "On My Mac"? (this will have the effect of removing it from the server, by definition).

Gmail is set for 30 days in Trash. ATT is random time. iCloud.com says 30 days. Maybe paid hosts usually have it set to never delete.

I'm not trying to fudge a work around. I've given suggestions to check settings on your devices. I've given you advise on how to store messages you don't want deleted. I'm not an Android user, but that could be the culprit.

You say there is a bug and pointing to Apple's OS, but you haven't proven where the messages are deleted from. Your computer is set correctly according to the images you posted. I doubt they were deleted from there.

If you need to prove which is doing the damage, disable the accounts from one device at a time to test. That way you can determine which is actually deleting the messages.

Can you disable that account in Mail and test by using webmail? That would prove or disprove Mail being the culprit.

If you think the user settings are corrupt even though they show correctly, you can reset the user defaults:

Remove Container file Mail:

Quit Mail.

In the Finder, select Go, then Go to Folder. Copy and paste the path below and hit GO:

~/Library/Containers/com.apple.mail

Move the whole com.apple.mail folder to the Trash, and open Mail and test. If all goes well, you can empty the trash. You may need to re create your user settings.

If there is a problem or you wish to restore the old file, first, Quit Mail.

Then open the Trash. Right click on the folder and choose Put Back from the menu.

You will need to recreate your personalized settings for Mail.

Note the above is for user settings and will not correct corruption in the Mail application outside of the user settings.

When you delete messages, they go the trash folder for the corresponding account. That will mean, for any IMAP account, they go to the trash folder on the server. Even if you see only one trash, they are actually separate by e-mail account.

OK. I saw where you stated you did a clean reinstall of OS, but I assumed you migrated your user account. Since it is doing the same as before, I don't see the point in removing any files.

If you changed the Trash to On My Mac, note that it still shows in the main Trash mailbox. It will be a local mailbox if it is acting correctly. The server Trash mailbox would be pushed out to the account in Mail's sidebar. You may have to expand the account in order to view the mailboxes there.

Did you verify this at the webmail site also as to what is happening to the messages?

In addition: The On My Mac mailbox shown in your trash is the trash folder for local mailboxes in general that don't belong to active accounts. The local account mailbox will still show in the Trash for active accounts with that setting.