The Messages app in OS X 10.8 Mountain Lion confuses the heck out of us because we never know where a given iMessage we send or receive will wind up. Some people are irritated at having an incoming message pop up on an iPhone, iPad, and multiple Macs all at once. There’s no hope for that, as Apple doesn’t yet let you set a single incoming device for iMessage based on where your eyeballs are focused at the moment.
But the contrary problem is also baffling: what if you can’t get iMessages to appear on all your devices registered with the same Apple ID? We figured out the issue, which can let you both turn on that “feature” or disable it. The key is “Caller ID,” a preference that appears when you have multiple addresses registered in Messages in Mountain Lion or in iOS. (For an iPhone, the phone number counts as an address, so even a single email address produces this option.)
In Mountain Lion, you find the Caller ID setting in Messages > Preferences > Accounts: select your iMessage account, and the Caller ID menu appears at the bottom if multiple addresses are registered. In iOS, look in Settings > Messages > Receive At > Caller ID to find it.
Caller ID defines what the iOS and Mountain Lion Messages apps use as the implicit “from” address when sending an iMessage to another party. When the other person replies, her reply is directed to your Caller ID address. That’s straightforward enough. But where it gets tricky is when you have a different set of email addresses associated with each iOS device and Mac.
For instance, let’s say Jeff has email@example.com, firstname.lastname@example.org, and email@example.com all associated with Messages in Mountain Lion on his MacBook Pro. On his iPhone, he has just firstname.lastname@example.org, and on his iPad, just email@example.com. (This isn’t just hypothetical; in the process of testing, he realized that he’d set up each device with different addresses.)
If Caller ID on Mountain Lion has firstname.lastname@example.org selected, when he sends a text using Messages, the reply will return only to his Mac. If Jeff changes Caller ID to his email@example.com address, then responses come to his Mac and iPhone; if it’s changed to firstname.lastname@example.org, then to his Mac and iPad.
Now, Glenn can send Jeff an iMessage to any of those three email addresses, and the note will come in to his Mountain Lion chat window. But when he replies, Messages in Mountain Lion always changes the from address back to his Caller ID address. If Glenn, in turn, replies to that reply and doesn’t change the recipient address, his responses go just to the devices associated with that email address. (In Messages, in the Messages window, you can hover over the person’s name after the “To:” label in a Conversation, and then click the downward-pointing arrow — not the name — to switch the account to which you want to address a message.)
This provides you with a couple of possibilities.
You can ensure that all devices receive all messages, by either making sure the same email addresses are entered or setting the Caller ID on each device to a common email address. For the moment, this is the most sensible approach for most people.
You could set up device-specific iMessage accounts and mark each as the Caller ID sender for its particular device. This is a little absurd, but it would work for enabling you to receive an incoming message on all devices, but have subsequent replies directed only to a particular device. For example, Glenn could set up email@example.com on each of his devices, so iMessages to that address would show up everywhere. But, if the Caller ID address for his Mac was firstname.lastname@example.org and his iPhone was email@example.com, responses to his iPhone-generated replies would come back solely to the iPhone. Similarly, when he initiates a conversation from a given device, his recipient doesn’t need to know that’s where it comes from; they just reply.
Of course, this second approach highlights one of the main frustrations with iMessage. If someone stores this device-specific address and creates a new message later — instead of replying to Glenn’s last message or using his general iMessage address — they may send it to a device he’s not using! Also, only iPhones can use a phone number as an iMessage account, so it’s entirely possible that a friend will send a text to Glenn’s phone number and ignore any previous iMessage conversation, thus forcing the conversation to go only to his iPhone.
So, although you may have a small measure of control over which address is sent with your outgoing messages, you still can’t dictate how other people always send messages to you without relying on just one address for all devices.
This all serves to demonstrate the missing pieces in iMessage. Apple seems to not want to provide centralized management of email associated with accounts, leaving that up to the individual device. But Apple does validate email addresses that are used with iMessage centrally, and confirms that each non-Apple ID address is associated with only one Apple ID account at a time. A little bit of help in clarifying what goes where, even if we need a Web site or preference pane to manage the information, would eliminate a lot of confusion and unnecessary fiddling.