POP3 is disabled by default in SugarCRM in favor of IMAP. However, if you need to use POP3 in your SugarCRM, you can easily enable it by adding the following line to the config_override.php file located in your SugarCRM main folder:

$sugar_config['allow_pop_inbound'] = true;

This will allow you to choose POP3 as Mail Server Protocol when creating mail accounts in SugarCRM.