After searching my system I found it:
# find / -name main.inc.php
/var/www/html/epesi/modules/CRM/Roundcube/src/config/main.inc.php
Changing:
$rcmail_config['identities_level'] = 3;
to:
$rcmail_config['identities_level'] = 0;
However I'm wondering if I'll need to do this for subsequent upgrades?
Thanks,
Andrew