I have a Gmail account with multiple aliases for work. On my iPad 4 and iPhone 5, I have it set up as an IMAP, not a Gmail account and the alias work fine. In Mavericks, I try to set up an email account under "Other" and it defaults to a Gmail IMAP account which doesn't support aliases for some reason. It doesn't let me set up an IMAP account if using a Gmail based domain. Our extension isn't @gmail.com, it is custom for the company, yet we use Gmail as the portal.
Anyone come across this and have you found a work around? Oddly enough, Googling it is no help.