Alchemy's Address Activity webhook tracks all ETH, ERC20, ERC721 and ERC1155 transfers. This provides your app with real-time state changes when an address sends/receives tokens or ETH. You can specify the addresses for which you want to track this activity. A maximum of 50,000 addresses can be added to a single webhook. Alchemy have multiple webhook types available, and this tutorial would also work for: Mined transactions, Dropped transactions, NFT activity and NFT meta updates.
At the end of this tutorial, we will have built a simple Express App that exposes an API to listen for ethereum address activity (e.g. ERC20, ERC721 and ERC1155 transfer events). Using the Alchemy Notify API, we will send notifications based on address activity via the Mailchain SDK to an Ethereum address.
We will use the Address Activity Webhook to send a mail to an EVM address or ENS name when a transaction occurs on the address.
The code for the webhook is based on the Authenticated webhook tutorial, which is not a prerequisite, but can be helpful to review.
You can find the full step-by-step tutorial here: https://docs.mailchain.com/developer/tutorials/integrations/send-mail-on-address-activity-alchemy-notify/