That I'm not 100% sure of. I know for receiving, you'd just configure OfflineIMAP to deliver each account's messages into a different folder, and just switch between them in Mutt, but I don't know how it would work for distinct from-addresses, contact lists, etc.

Some quick googling[1] makes it look like you indeed do that first thing, and then set up a hook to load a different configuration file when you enter the folder for a different mailbox.

[1]: https://www.df7cb.de/blog/2010/Using_multiple_IMAP_accounts_...