In Gmail you now have the option to only send your vacation response to other people in your domain and not to external recipients.
Editions included:
Standard, Premier, Education, Partner Edition and Google Apps for Government
Languages included:
All languages supported by Gmail
How to access what's new:
In Gmail, go to ‘Settings’ -> ‘General’ -> ‘Vacation responder’ section, and select the new option to only send a response to people in your domain.
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