Why and When Do Email Accounts Expire?

Email addresses are not permanent. In fact, a historically active email address may suddenly croak—without warning or a farewell note—much to an email marketer's dismay.

Such email addresses that vanish into the ether do come with a somewhat bland obituary, though, in the form of a non-delivery report (NDR). The NDR generally indicates a useful yet enduring error, such as: "no such user";  "mailbox not found"; "the mailbox has been deactivated"; "the recipient has moved on so please stop mailing". (OK, I may have made up the last one.) These are what are known as hard bounces.

Hard bounces indicate an invalid email address or an address that is no longer in use. For this post, we'll focus on the latter case as it applies to webmail accounts: Why do some email addresses at popular webmail providers, such as Gmail, Hotmail, or Yahoo!, suddenly become undeliverable?

Here are the most common reasons why a once-valid email address might be deactivated. 

1. The user has chosen to close the account. It's easy to open a webmail account, and it is just as easy to close one. Users who decide to ditch their existing email address usually have an online, self-service option to permanently deactivate their mailbox with any of the top webmail providers.
2. The account has been deactivated for abuse. Webmail accounts are governed by the provider's Acceptable Use Policy (AUP) or Terms of Service (TOS). If a particular account has been investigated and verified by the webmail provider to violate their AUP or TOS, that account may be terminated immediately if the violation warrants it.
3. The email account has turned dormant. Webmail accounts are free to register for, but they do come with storage and other costs to their providers. As such, most providers periodically deactivate accounts that are no longer used. Specifically, if an email account has not been logged in to for a certain period of time (more info on specific timeframes below), then that account will be deemed dormant and will be a candidate for automatic deactivation. The routine purging of inactive accounts from the system helps providers maximize their resources. 

As one of the tenets of list hygiene is to stop emailing an address that results in a permanent error (aka hard bounce), this information can help senders understand why there is constant attrition within their mailing lists. Furthermore, here's specific guidelines on when popular providers deem an account as dormant and, therefore, eligible for deactivation:

AOL = 90 days of inactivity

• "Your username and account may be terminated if you do not sign on a Service with your username at least once every 90 days."
• Via http://legal.aol.com/terms-of-service/full-terms/

Gmail = 9 months of inactivity

• "Google may terminate your account in accordance with the terms of service if you fail to login to your account for a period of nine months."
• Via https://mail.google.com/mail/help/intl/en/program_policies.html

Hotmail = 270 days of inactivity

• "Your Outlook.com or Hotmail account will become inactive if you don't sign in for more than 270 days or within the first 10 days after signing up for your account."
• Via http://windows.microsoft.com/en-US/windows-live/account-close-account

Yahoo! Mail = 6 months (or more) of inactivity

• "Yahoo! Mail accounts are deactivated and removed after six months of not being used, plus an additional two months for each year you held the account."
• Via http://help.yahoo.com/kb/index?locale=en_US&y=PROD_ACCT&page=content&id=SLN3057
• BT Yahoo! Mail, the Yahoo-powered email service for customers of BT (a UK ISP) has recently stated that their inactivity period is set to 150 days.