IPhone 4 don't sync

[nashwa_sowelam@avit.com.eg]

Hi all

when configuring Iphone version 4 to sync with zimbra server version 6.8 2678
it displayed this message "can't find exchange server"

I filled the following
username:nashwa_sowelam
domain:avit.com.eg
server :mail.avit.com.eg
e-mail:nashwa_sowelam@avit.com.eg
and for sure the password I don't hot to trobleshot that issue
when press next it displays "can't find exchange server"

note that the account is allowed to sync using the mobile
also HTC mobile is syncing with zimbra servers