Microsoft Exchange and Office 365 offer an option to notify senders when their recipients open and read emails they've sent.
If you have a backlog of 'Unread' emails in your Inbox and SaneBox processes relocate some of them to new Sane mail folders like SaneLater, sometimes the Exchange mail server mistakes this for the items having been trashed when that's not what has happened at all.
In other words, when the unread emails are moved from the inbox to another folder, having originally been sent to you with a “Read Receipt Required” condition set, the automated Exchange server processes mistakenly send out an emailed notice back to the original sender with a faulty status update for the message.
This email read-receipt sending activity is not generated by SaneBox. Our systems have no control over the settings your Exchange email server administrator decides to use, or the "Read Receipt Required" criteria that certain senders enact when writing to you.
Chalk this up to a chance to laugh about how computers aren't as smart as we'd like them to be and maybe use it as a conversation starter.
Please note that in some cases (If allowed by your administrator's Exchange server settings) you can control responses to read-receipt requests from in your own email software, as described here for Outlook 2007, Outlook 2010, and Outlook 2013.
Other solutions can be found here: https://www.gfi.com/support/products/Journal-mailbox-generating-Non-Delivery-Reports-when-using-GFI-MailArchiver-with-Microsoft-Office-365