Email client cant search email body - IMAP limitation?

I am using Missive email client in my business, but it does not search within the email body.

The Missive team say this is a limitation of the IMAP server and Dovecot. Gmail will work OK they say, but I dont want to use GMail due to other issues.

Does anyone at Virtualmin know about this, and what needs to happen to allow the search to search within the message body? Something need to happen in Dovecot? Somthing about FTS and FTS Solr?