Apple’s iMessage service is its proprietary messaging technology, which works through iCloud to allow the synchronization of conversations between all supported iOS and Mac OS devices. This is convenient, because you can chat and text on any of your Macs, iPhones, or iPads, and then continue the conversation on another device, with full access to the conversation history.

In addition to syncing, iMessage should allow you to seamlessly use multiple means of addressing the members of a conversation, so for instance, you can send a reply to a person’s phone number or to his or her e-mail address, and that reply should be appended to the same conversation (provided the person has allowed both of those to be used in iMessage).

While this should be the case, there are times when your devices might not sync up properly, resulting in one or two frustrating behaviors:

1. Conversations do not show up on one or more device
2. Messages sent from different devices are split into different conversations
3. Inability to send from a specific e-mail or phone number
4. The inability to receive a message sent to a specific e-mail or phone number

This type of problem can be frustrating, because if one device is configured incorrectly, then it may be difficult to find it. The problem could be with your iPhone or your Mac, or those of the person (or people) you are communicating with.

To troubleshoot this, first check Apple’s iCloud system status to see if there are any problems Apple is aware of with its iMessage service. While this status monitor is not always accurate, it can sometimes inform you of known problems. If a problem is showing on this site, then wait for the site to show an all-clear on all services before continuing troubleshooting. Even though iMessage is the most relevant of the services listed, if others (such as Apple ID or iChat) are experiencing problems then there may be a domino-effect of problems into other services.

If Apple’s services all check out, then try a new conversation with a second individual, to see if the conversation syncs properly with that person. If so, then the issue is likely with the account or configuration with the person you were initially contacting.

On the other hand, If you see similar problems of split conversations or connectivity issues with other individuals, then the problem is likely on your end.

In either of these cases, the holders of the problematic accounts should try resetting their connections to iMessage on each of their Macs, by logging out and logging back in. Note that this is not done in Apple’s iCloud system preferences, but rather in the Messages program itself:

1. Go to the Accounts section of the Messages program preferences.
2. Select your iMessage account that uses your Apple ID.
3. Click the Settings tab, and then click Sign Out.
4. Now sign back into iMessage.
5. Repeat this for all Mac OS systems configured with your iCloud account.

When done for all individuals with affected accounts, try creating a new conversation and see if it syncs properly.