Do you have hidden Outlook rules that you need to remove from your system because it is sending some or all incoming emails upon receipt to your Deleted Items folder? I have seen this issue many times (due to malware sneaking onto the client’s computer) and were fortunate to have it resolved upon each occurrence.
When you check the rules area in Outlook, you will typically see the “There are rules created with a different Outlook or a Outlook Web Access that are not shown” which indicates that the malware created the rule and then hid it to make sure that it goes unnoticed.
Before following my removal instructions, you should export (as editable text) the rules that are currently saved as you can import them later on instead of re-inputting manually. This is helpful if you have been creating rules for years and do not want to take hours to recreate them.
Removing Hidden Outlook Rules
Please close Outlook and then try and bring up the Run window. Once the Run window is visible, type in outlook.exe /cleanrules and submit the command to execute. Once the process is over, you can then reopen Outlook and see if the yellow triangle is gone.
Now that your hidden rules have been removed from Outlook, try and send an email to yourself (or a contact that was being filtered) and see if it still ends up in the Deleted Items folder. If it is fine, you can import any rules that you had backed up (after manually editing out the malware rules) and have another email submitted to yourself. If there no further issues after the import, then your issue has been resolved. You will now want to see if any rules that you no longer need can be deleted then make a new backup or safekeeping.
Why It Happens
Malware gets onto your computer and then attempts to send phishing emails to your contacts and other users whose email addresses were harvested from databases. Some email accounts (especially the free ones) will be disabled for a new one when the user starts to get spam so when the malware on your computer tries to send an email to those accounts or your contact with an autoreply turned on, you will see that your account is compromisedby the alert email in the inbox. To make sure that those reply emails go unnoticed, the rules send the email to the deleted folder as soon as it arrives.