I want to get announcement on smart speaker as and when amazon packages are delivered.
One way is to connect emails to home assistant and setup automations. Is there any other better idea?
Depends what the objective is. If you want to avoid leaving parcels on the doorstep, email detection is probably a bit hit and miss.
I believe some video doorbells have a “parcel detection” feature - you could try Reolink first, as they’re now “works with”.
I use the emails to trigger an announcement. I don’t think I’ve missed any due to unreliability. But I’m also not around for all of them either so… 
Depending on the carrier, you might get close to real time emails from Amazon about deliveries, such as it’s own carrier has that feature.
Some other carriers relies on industry standard messaging protocol (EDI) and it might be delayed up to couple of hours to receive the email notification from Amazon for those ones.
And you’re relying on the efficiency (and honesty) of the courier. With a camera you’ve got your own data.
I’ve been using the Mail and Packages custom integration for a year or two and had great luck; the only real delay is that you’re only checking email every few minutes.
I’m in the US, so almost all Amazon packages come either from them or USPS and I always get notified basically right away (outside of those rare instances where tracking goes haywire, but then that applies to everything including the Amazon website). FedEx and UPS also work well. The main issue with Amazon, is if they ship via another carrier the package counts can get duplicated or confusing. But for delivery notifications, this generally just means getting notified multiple times.
You can use the phone app’s ability to expose phone notifications as a sensor. If you use the phone Amazon app, you will likely receive a phone notification that the parcel has been delivered.
You can also incorporate watching for any beacon trackers that appear close to your home from their handheld devices, the driver’s vans and their personal phones.
I use a door sensor on my mailbox and a deck box but the drivers do not always reliably deliver to these places.
My experience with this is that trying to setup notifications confirming a delivery are often delayed, sometimes up to an hour. So it really defeated the purpose and I deleted the integration I used.
In my experience the delays may be down to the delivery driver. Most who drop off to me are scanning the packages at the door and marking them as delivered. Some do it in the van prior to placing them at the house, some clearly do it when returning to the van, or worse… When they have completed all deliveries.
I expect that in more rural areas availability of a cell signal may also contribute to delays.