Please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

Thanks for replying! I didn't paste ALL the information (about printers, etc.), but I think this maybe what you're looking for. It's information specific to the AOL account to which I'm referring. (please let me know if you need anything else. Thanks again!):

BEGIN PASTE

 Application Basics

   Name: Thunderbird
   Version: 52.5.2
   User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2
   Profile Folder: Open Folder

             (Local drive)
   Application Build ID: 20171221110448
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory
   Profiles: about:profiles

 Mail and News Accounts

       account31:
     INCOMING: account31, , (imap) imap.aol.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.aol.com:587, alwaysSTARTTLS, passwordCleartext, true

END PASTE

Open Tools/Account Settings, then look under Server Settings for the AOL account. What do you have for 'When I delete a message'? It should be 'Move it to this folder', Trash on <AOL account name>, where 'AOL account name' is the name that appears in the Folder Pane.

Thanks so much for your help! At first, this didn't seem to be working, but now it is. Really appreciate the input! Happy New Year!