I just use multiple "accounts", they don't necessarily need unique SMTP/IMAP settings. With more than one you get to pick a From: via drop-down in Compose, and

I just use multiple "accounts", they don't necessarily need unique SMTP/IMAP settings. With more than one you get to pick a From: via drop-down in Compose, and you can also set (per-folder) the default account and/or CC:/Reply-to: