If you've fallen out of favor with one of your Google Chat contacts, getting back into their good graces may be harder than you think. Google does not send you any sort of notification once you have been blocked, and no warning or error messages will be displayed if you begin a chat with that contact. To you, it will simply appear that they are offline. A quick solution is to use a universal chat client to determine whether one of your contacts has blocked you or is simply on hiatus. Chat client options include Pidgin, Trillian and Meebo.
Configure your universal chat client to connect with your Gmail account. The steps for this will vary depending on which program you are using.
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Set your chat client to display all of your offline contacts. As Google Chat will display a contact who is blocking you as offline, they will appear within this group even if they are currently signed in.
Select your contact's name from the offline contacts list. Right-click on their profile name. Select the option that allows you to view their contact profile. If the user is simply offline, you will be able to see their Gmail address. If no information is present within their profile, then that user has blocked you.