http://monerotoruzizulg5ttgat2emf4d6fbmiea25detrmmy7erypseyteyd.onion/resources/user-guides/multisig-messaging-system.html
If another signer tells you that a particular message did not arrive or was lost somehow you can send it again anytime, picking it from the message list, like you would re-send an e-mail in a similar situation. Signers and Messages So, where a "normal" Monero wallet without MMS simply told manages three types of data (addresses, accounts and transactions), the MMS adds two more: Signers and messages.