“These accounts are often vulnerable,” Ms. Kricheli said, “and once an account is compromised, it can be used for anything from identity theft to a vector for unwanted or even malicious content, like spam.”

The policy went into effect on Tuesday, but the company said it would not begin deleting unused accounts until December at the earliest. Google said it would start by purging accounts that were set up but never used.

Before an account is deleted, Google said it would deliver several notifications to users through Gmail and any backup email addresses that had been provided.

Ms. Kricheli said the plan to expunge inactive Google accounts only applied to personal accounts and would not affect organizations like schools or businesses that use Gmail and other Google services.

Google users who have not used their account in at least two years and do not want their account to be deleted can keep it active by simply signing into Gmail or any other Google service, such as Google Drive, YouTube or Google Search, or by downloading any app from the Google Play Store.