Problem in downloading all mails in webmail to outlook

Problem in downloading all mails in webmail to outlook

We have properly configured our zoho mail account with outlook. But all the mails in webmail can't be seen in outlook inbox. (oldest emails are not downloaded properly ). We kept the outlook open to download all the mails for days, but still some are missing.

Please tell us to download all the mails in webmail to outlook inbox.

Thanks