While hard bounces typically indicate permanent delivery failures, numerous factors can lead to a previously hard-bounced email becoming deliverable again. These include user-initiated actions like reactivating inactive accounts (particularly with free email providers such as Microsoft, Gmail, and Yahoo) or correcting typos. Technical issues like temporary server problems, DNS errors, MX server disconnections, and full mailboxes can cause hard bounces that resolve when the underlying problems are fixed. Additionally, improvements to sender reputation, email authentication practices, and content quality can improve deliverability. In some cases, spam trap conditioning involves a period of hard bounces before the trap becomes active. ESP definitions of hard bounces vary, and a tolerance for multiple 'user unknown' bounces was previously accepted. However, prior hard bounces can impact sender reputation and require cautious re-engagement strategies. Certain providers, like Yahoo, may have recurring hard bounce issues that senders need to accommodate.
11 marketer opinions
While hard bounces generally indicate permanent email delivery failures, several scenarios can lead to a previously hard-bounced email address becoming deliverable again. These include the recipient reactivating an inactive account (particularly with free email providers), resolving temporary server or DNS issues, fixing typos in the email address, clearing a full mailbox, or rectifying issues that caused the recipient's server to block delivery. Sender reputation, content quality, and proper email authentication are crucial for overall deliverability and can influence whether an address becomes receptive again. Maintaining a clean email list is essential to mitigate the negative impact of bounces on sender reputation.
Marketer view
Email marketer from Neil Patel explains that a hard bounce indicates a permanent reason why an email cannot be delivered, such as a nonexistent email address. However, they also note that deliverability can fluctuate. Factors such as sender reputation, content, and authentication play a role, suggesting that improvements in these areas could potentially make an address deliverable again if the initial hard bounce was due to temporary issues.
20 Jun 2022 - Neil Patel
Marketer view
Marketer from Email Geeks explains that Yahoo used to hard bounce deliverable messages periodically. The SMTP non-deliverable message should be read to determine if it's a real failure, and the sending server should accommodate 5XX responses.
8 Sep 2021 - Email Geeks
8 expert opinions
Experts highlight various situations where a hard-bounced email address can become deliverable again. These include temporary server errors (resulting in incorrect 5xy responses), user account reactivation after inactivity (especially with free providers like Microsoft), resolution of MX server issues, and clearing of a full mailbox. Spam trap conditioning can also lead to reactivation after a period of hard bouncing. Billing issues and temporary DNS problems represent other scenarios where resolution can restore deliverability. It's important to note that historically, a tolerance for multiple 'user unknown' bounces was accepted by ESPs and ISPs. However, the original bounce could impact sender reputation.
Expert view
Expert from Email Geeks explains that organizations sometimes condition spam traps by hard bouncing mail for 1-2 years before activating them. Mailing these addresses can have consequences.
4 Aug 2023 - Email Geeks
Expert view
Expert from Email Geeks shares that free mail providers sometimes stop accepting mail for inactive addresses, but the addresses reactivate when the user logs in again, Microsoft is a big one for this.
13 Apr 2023 - Email Geeks
4 technical articles
Documentation sources generally agree that hard bounces signify permanent delivery failures. However, they also acknowledge circumstances where previously undeliverable addresses can become viable again. These scenarios include the recipient correcting issues like typos in their email address or an inactive account being reactivated after a period of dormancy. Underlying technical issues such as network or server configuration problems, if resolved, may also restore deliverability.
Technical article
Documentation from Mailgun defines a hard bounce as a permanent reason why an email can't be delivered. However, they suggest that if the recipient takes action (like correcting a misspelled email address), the address could become deliverable again.
2 Dec 2023 - Mailgun
Technical article
Documentation from Microsoft says that addresses that hard bounce due to an inactive account may become deliverable again when a user logs in after a period of dormancy and the account is reactivated by the provider.
5 Jan 2025 - Microsoft
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