Unfortunately it’s not possible to export (IMAP) email body’s onto Excel using the Export feature in Outlook.

As a work around, you may export the particular IMAP folder emails as .PST format and then open the same file in Outlook.

To open the PST file, click on file->open->browse to the PST file->click open.

To Export the file, Click on on File > Export to file->Microsoft Excel>Select the PST file.