If you try to setup a filter that automatically forwards messages to an email address, Gmail now requires to verify that it's yours. After adding the forwarding address, Gmail will send a message to that address and you'll need to click on a link to show that you have access to the email account.
Google says that there are exceptions to this rule for the users of Google Apps Premier and Google Apps Education, which don't need to verify forwarding addresses for their own domain.
You can autoforward messages by defining a filter or by using the forwarding feature from Gmail settings. Gmail allows users to create up to 20 filters that forward to other addresses.
It's likely that the autoforwarding feature was used to send spam, so these restrictions will hopefully decrease the number of spam messages sent from Gmail accounts.
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