Email visible in webmail, but nothing visible via IMAP

Email visible in webmail, but nothing visible via IMAP

I imported a large number of old email messages via zip'd eml files to various folders, including old Sent messages, Inbox and such. All these emails appear when using the webmail interface, but no messages are visible via IMAP. I have tried disabling/re-enabling IMAP, turning off/back on the folders, etc but the messages just aren't visible through IMAP. This occurs on both desktop and mobile IMAP clients. Any suggestions?