In the event that you’re unfortunate enough to trigger the message in your mail client (either due to invalid password attempts or spamming the Get Mail button), the fix is fairly simple.
…and replace yourwebsite.com with your actual website name. Regular GMail customers who trigger that issue can head to https://www.google.com/accounts/DisplayUnlockCaptcha instead.
Either way, you’ll have to enter your correct password and answer a Captcha. Credit for this tip goes to mydigitallife.info.