Sent box download issue

Sent box download issue

Dear team,

We shifted all mail from X hosting provider to your server. For saving space , based on your documents we set POP with delete once download option but mails were downloaded only Inbox not sent mails. Still many mails in sent box on zoho portal. 

I would like to know the reason for not deleting mails. 

I set 15 days - older mail delete from server in Thunderbird mail application.

Please help me to fix this issue since 99% mail box full.

Email account -  swati@eshitarubber.com