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.
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
Gmail = 9 months of inactivity
Hotmail = 270 days of inactivity
Yahoo! Mail = 6 months (or more) of inactivity
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