Why did 50k Yahoo email addresses bounce with a disabled mailbox error after ESP migration?

Email marketer from StackExchange answers that an ESP migration can trigger a surge in bounces due to differences in how each ESP handles suppressed or inactive addresses. It's crucial to ensure that the new ESP has an accurate and up-to-date suppression list, or the sender risks emailing disabled or invalid accounts.

Marketer from Email Geeks advises using the official Yahoo sender channel and doing due diligence by checking lists, collection methods, and engagement before contacting the postmaster team.

Email marketer from Quora explains that a 'mailbox disabled' bounce typically means the email address is no longer valid. In the context of an ESP migration, this often points to issues with list cleaning and suppression management, where outdated or deactivated addresses weren't properly removed.

Marketer from Email Geeks asks if this was the first send after migrating from ConvertKit, suggests verifying if the bounces are just previous bounces or cold subscribers, and checking if both ESPs classify bounces the same way. Also suggests checking if data was malformed during transfer.

Email marketer from MailerQ explains that a 'disabled mailbox' error from Yahoo often means the recipient's account is no longer active or has been closed by the user or Yahoo. After an ESP migration, these addresses might surface if the previous ESP didn't provide a complete suppression list or if the list hygiene practices weren't stringent.

Email marketer from EmailVendorSelection explains that a 'mailbox disabled' bounce means that the receiving server has determined that the email address is no longer active and to confirm with the user. An ESP migration could cause these issues if old or unengaged addresses are re-introduced.

Marketer from Email Geeks suggests that Yahoo may have done a cleaning and disabled a bunch of old accounts, which could explain the bounces.

Email marketer from SocketLabs shares that a 554 error, like the 'mailbox disabled' error, typically indicates a permanent failure. This can happen if the user's account has been closed due to inactivity, policy violations, or other reasons. An ESP migration might expose these issues if old or unengaged addresses are re-introduced.

Email marketer from Reddit shares that after migrating ESPs, a sudden increase in bounces, especially with 'mailbox disabled' errors, could indicate that the old ESP's suppression list wasn't fully transferred or was corrupted. It also suggests that the previous ESP might have automatically suppressed addresses that were inactive for a certain period, and those addresses are now being re-introduced.

Marketer from Email Geeks recommends checking prior engagement (before 30 days), confirmation opt-in method, and if engagement was through a different ESP. Also suggests sending individual test emails to see if they deliver or bounce.

Marketer from Email Geeks suggests the option to resend to the bouncing addresses or not. Suggests a small test batch or 1:1 outreach before sending to all. Recommends contacting Sender Support in case it was an error on Yahoo's side.

Email marketer from Mailjet explains that hard bounces, such as 'mailbox disabled', indicate a permanent reason why an email cannot be delivered. After an ESP migration, these errors can arise if the old suppression list wasn't fully transferred or if outdated addresses were included in the new campaign.

Expert from Email Geeks suggests the migration process needs to be looked at. Addresses may have been previously suppressed by the original ESP because of temp failures or abandonment. The lack of clicks/opens indicates the addresses have likely been abandoned for a while. Suggests the previous ESP may not have extracted all bounced addresses.

Expert from Word to the Wise (based on information from multiple pages, synthesized as there isn't a single dedicated page) explains that a likely cause is poor list hygiene. Post ESP migration, these problems often surface because older addresses are re-introduced without proper verification, or suppression lists aren't migrated properly. The 'mailbox disabled' error indicates that the address is no longer valid, suggesting the need for stringent list cleaning practices before and after migration.

Expert from Spam Resource (based on synthesized information from the site) explains that a high volume of 'mailbox disabled' bounces post-migration suggests issues with suppression list handling during the transition. It also might mean that the new ESP is stricter about bounces and is highlighting pre-existing issues from before the migration.

Documentation from RFC Editor specifies that a 5.x.x status code indicates a permanent failure. A 'mailbox disabled' error falls under this category, meaning the address is no longer valid. After an ESP migration, if previously suppressed addresses are inadvertently re-introduced, these errors would occur.

Documentation from Microsoft explains that Non-Delivery Reports (NDRs) including a 'mailbox disabled' or similar error indicate a permanent delivery failure. An ESP migration could expose these issues if historical data is not properly managed or suppression lists are incomplete.

Documentation from Yahoo Postmaster emphasizes the importance of list hygiene for bulk senders. Disabled mailboxes should be promptly removed from mailing lists to maintain a good sender reputation. ESP migrations should ensure accurate transfer of suppression lists to avoid sending to invalid addresses.