Mail reciveing from internal zoho accounts but nor from gmail , or some times it reciveing after 2 days

Mail reciveing from internal zoho accounts but nor from gmail , or some times it reciveing after 2 days

Dear sir, 

First of all thanks for such an superior service from zoho.

I am facing issues in zoho mail account to receive mail from gmail or any other web-mail, or sometimes it deliverers after 2 days, but from zoho accounts its getting instantly,

my domain is : itechgrow.com

please do needful

thanks in advance