The account <my email account> has been configured in Zoho Mail for fetching mail via POP. The total number of mails has exceeded 50000 mails for your mailbox in the POP server. ZohoMail can start fetching again if your settings is changed to "Delete mails in server when received here". But this change in the setting might delete the mails from your server permanently, based on your Mail Server behavior.
Kindly check with your Mail Service Provider regarding the deletion behavior when mail fetched via POP is marked for deletion before you update the settings. PYou can reach to us at support@zohomail.com, if you need any further clarifications.