To send and receive messages with Mailchain on Algorand, you will need to add an existing account (or create a new one and save the 25 word mnemonic phrase).
mailchain account add --protocol=algorand --network=[NETWORK] --private-key-encoding=mnemonic/algorand --private-key=[PRIVATE-MNEMONIC-STRING-VALUE] --key-type=ed25519
--network=mainnet or a testnet you are working on.
--private-key-encoding=mnemonic/algorand is the encoding used for supplied private key
--private-key is the 25 word mnemonic phrase of your account to be able to sign and decrypt messages.
--key-type=ed25519 (for Algorand).
By default, Mailchain comes preconfigured with some default values to make it easier to get started. Algoexplorer is configured by default to query the received messages.
To change the API lookup settings in the Mailchain Client, follow the instructions here: Mailchain Settings: Viewing and Updating