What is the cpanelsolr process?
cpanelsolr is the software that manages the Dovecot text searches for both Roundcube and Horde. This was added in cPanel version 64.
Fast Email Searching (IMAP Full Text Search)
Full-Text Search Indexing (powered by Solr) provides fast search capabilities for IMAP mailboxes. Users of iOS devices, Microsoft® Outlook™, SquirrelMail, Horde, Roundcube, and Mozilla™ Thunderbird will notice significantly improved search speed and convenience.