PrestaShop Customer Service Page not working

On a PrestaShop site on clicking Customer Service link on the left menu, the page failed to load, it stuck at loading for a while, then show error message,

This is because a connection to the IMAP server is not able to establish. To fix the error modify IMAP-related entries in ps_configuration table.

To list all IMAP related entries, run

select * from gult_configuration where name like 'PS_SAV_IMAP%';

To remove values for IMAP settings, run the following SQL commands.

update ps_configuration set value='' where name='PS_SAV_IMAP_URL';
update ps_configuration set value='' where name='PS_SAV_IMAP_PORT';
update ps_configuration set value='' where name='PS_SAV_IMAP_USER';
update ps_configuration set value='' where name='PS_SAV_IMAP_PWD';

Once you removed IMAP related entries, you can reconfigure IMAP by going to

PrestaShop Admin >  Customer Service >  Customer Service

Scroll down, you will see Customer service options.