When creating events using Icelander or Zoho mobile, email notifications are not getting sent to the invitees

When creating events using Icelander or Zoho mobile, email notifications are not getting sent to the invitees

I am trying to add an even and trying to add people to it. The event is successfully created but the invitees are not getting any email notification regarding it. They are receiving emails only when creating the event as meeting and over the web calendar.