Auto delete sent items in the webmail when I installed Thunderbird email client

Auto delete sent items in the webmail when I installed Thunderbird email client

Hi 

i need assistance for this concern.
how can i retrieve the old sent items started July 2017 up to April 17 2017?
cause as i installed the Thunderbird Application and configured it with IMAP and POP access the auto delete of sent items took place. 
could you help me to this.

Thank you.