Our IMAP mail servers now support the IMAP LIST Extension for Special-Use Mailboxes. That means we send hints to your IMAP mail program suggesting it should store copies of sent and deleted mail in the “Sent” and “Trash” mail folders on the server, rather than a different location the program might randomly choose.
Without the hints, some mail programs default to storing copies of sent and deleted mail only on your local computer or device. Those copies can’t be seen by other programs or devices, and they aren’t saved in our backups. You could always change that manually, but with the hints, some mail programs — particularly macOS Mail and iOS Mail — will now automatically save the mail to server folders with no extra configuration needed. The copies will then be visible on all the IMAP devices you use, and they’ll be saved in our backups.
What if I don’t want my mail program to use these folders?
In our testing, this change doesn’t affect mail programs that are already storing sent and deleted mail on the server in folders you’ve specified. But if your mail program does change where it stores sent or deleted mail, and you don’t like the change, you can use your program’s settings to explicitly choose where you want sent and deleted mail copies to be stored (for example, this page describes how to set folders on an iPhone or iPad, and this page describes how to change folders for the macOS Mail program).
If your program doesn’t offer that feature, another option is to delete the “Sent” and “Trash” server folders from your mailbox (or ask us to do so). That will prevent any hints from being sent at all, making things work exactly as they did before.