There are several reasons why you might receive a 'Successful Login from New IP' email alerting you to a login from a new IP address. You could be logging in from a new location that’s utilizing a different network from your own (café, library, friend’s house, mobile device, etc.) or using a VPN which can change IPs in short intervals. If none of these apply, immediately log in to your account and check your login history. If you find unrecognized logins in your login history, you can self-freeze your account by returning to the 'Successful Login from New IP' email and clicking on the link, “freeze your account.”
While the account is frozen, you can still log in but cannot trade or withdraw. If you don’t already have 2FA enabled, we recommend you do this now. To learn more about enabling 2FA, read the 2FA setup article.
Next, create a support ticket and set the ticket type to "Compromise/Breach" only after taking the steps outlined above, and a support agent will help you re-enable your Poloniex account safely.