If you use an address book, Apple Mail can be very aggressive about auto-completion, to the point that your ability to send messages to an arbitrary address ends up being seriously compromised. There’s a simple workaround to this problem: enclose the address in angle brackets, e.g. <firstname.lastname@example.org>.
There’s an old discussion thread on apple.com (without any resolution) about this, but not much else, so I figured I’d put it up here just in case it gets indexed and ends up being useful to someone.
Yes, I’m using Apple Mail again… for now… and only on my new work computer. That’s because others there report it interoperates better with their mail server than Thunderbird. I have the sneaky feeling that I’ll bail on Apple Mail within a month or two, but might as well be a good sport and give it an honest chance.
Keywords: Apple, Mail, address book, autocomplete, disable.