This is my mutt configuration.
I use two accounts, one gmail the other gmx. I keep them synced to a local maildir via offlineimap and do my sending for either account via msmtprc. Examples files for these two tools are present.
I also use folder hooks to set up any account-specific settings when you navigate to a directory for that account.
I use uber-mutt which is basically mutt with the sidebar-patch and a forgotten-attachment patch. It is in the AUR.
Be sure to
man muttrc for anything you don't understand.