---

IMPORTANT UPDATE:

Starting Q1, 2024, Yahoo will require that all bulk senders:

• Authenticate their email: To help our users be more confident about an email’s source, we will require senders to implement stronger email authentication leveraging industry standards such as SPF, DKIM and DMARC.
• Enable Easy Unsubscription: Our users should be able to unsubscribe from unwanted emails without any hassle. It should just take one click. While we have promoted solutions for some time, adoption of these common-sense standards have been low. We will require senders to support one-click unsubscribe and honour our users' requests within two days.
• Only send emails our users want: True to our key mission, we want to ensure our users’ inboxes are not cluttered with unsolicited or irrelevant emails. While we have measured user-reported spam rates for some time and even exposed some of that data for trusted senders, we will start enforcing a threshold to ensure our users can continue to enjoy a spam-free mailbox.

In the coming months, Yahoo will provide more details about these new criteria. Meeting these new requirements before Q1 2024 may improve your email delivery.

Market share and history of MBP

Yahoo Mail was launched by Yahoo in 1997 as an extension of its existing web portal. The idea behind Yahoo Mail was to provide users with a free and accessible email service that could be accessed from anywhere with an internet connection.

At the time of its launch, Yahoo Mail offered a significant advantage over other email services by providing users with a generous storage capacity of 4 MB, which was much larger than what its competitors offered.

More recently, Yahoo has faced many challenges and competition in the email market, particularly from services like Gmail, however despite these challenges, Yahoo Mail has continued to provide its email services, and the company has made efforts to improve security and enhance the user experience. Yahoo Mail remains one of the popular email providers globally, offering free email accounts and various features to its users.

Anti-Spam Measures

To protect its messaging infrastructure, Yahoo uses some public blocklists such as Spamhaus and SURBL.

Feedback Loop

The Yahoo Complaint Feedback Loop (CFL) program is a free service offered to email senders to minimize complaint rates and improve their sending reputation. It only supports emails signed with a DKIM key. The CFL program is domain-based and no longer offers IP or CIDR-based feedback loops.

Click on the following link and then click on 'Enroll Now' at the end of the page to access the registration form: https://senders.yahooinc.com/complaint-feedback-loop/

Email Deliverability & Performance Feeds

Similar to Google’s Postmaster Tool and Microsoft’s SNDS, Yahoo also has a (paid) Deliverability & Performance Feed. The Placement Feed provides metrics on how many emails from a sender domain are delivered to the inbox, spam, and folders. It also provides metrics for error and complaint counts.

The Campaign Performance Feed provides key metrics such as delivers, opens, reads, glances, skims, deletes, and clicks for a sender domain. Metrics are broken down by sender domain and campaign.

Yahoo Postmaster Technical & SMTP Tweaks

Yahoo suggests the following best practices to optimize delivery to its infrastructure:

• Send Emails customers want
• Authenticate using SPF, DKIM, and DMARC
• Segregate Email types by IP or DKIM domain
• Use OPT-IN method to confirm user subscriptions
• Allow users to easily unsubscribe
• Remove invalid recipients
• Enroll in complaint feedback loop (CFL)
• Publish reverse DNS (PTR) records
• Ensure mail servers are secure
• Control the flow of your outbound emails
• Be compliant with RFCs and CAN-SPAM

Unlike the majority of mailbox providers, Yahoo accepts 20 emails per connection. Further emails should be sent by opening a new connection, otherwise deferrals will occur.

It is also a common practice to double DKIM sign all email traffic with your own domain, as Yahoo's complaint feedback loop is not IP, but domain based. This way, you don't need to sign up for the complaint feedback loop whenever a new domain is used.

It is also worth mentioning Yahoo's View Time Optimization program, which can considerably increase user engagement. VTO emails, regardless of when Yahoo receives your email, will pop up on top of the recipient's mailbox only when the recipient accesses his mailbox. This way your email is not stacked up by newer ones.

Common Error SMTP Messages

421 4.7.0 [TSS04] Messages from xx.xx.xx.xx temporarily deferred due to unexpected volume or user complaints - 4.16.55.1; see https://postmaster.yahooinc.com/error-codes

The above error typically occur when the sender has a poor reputation or no sending history.

451 Message temporarily deferred due to unresolvable From header domain xxx.com. See https://senders.yahooinc.com/error-codes#invalid-from

554 Message permanently deferred due to unresolvable From header domain xxx.com. See https://senders.yahooinc.com/error-codes#invalid-from

554 Message permanently deferred due to unresolvable RFC.5321 from domain. See https://senders.yahooinc.com/error-codes#unresolvable-from-domain

The above errors occur when the FROM address or domain are invalid.

554 This mail has been blocked because the sender is sending too much mail for its authentication status. Please set up DKIM aligned to the From: domain. See https://senders.yahooinc.com/smtp-error-codes#authentication-failures for more information.

The above error occurs when emails are not properly authenticated.

554 5.7.9 Message not accepted for policy reasons. See https://senders.yahooinc.com/error-codes

The bounce message refers to a non existing recipient. Such recipients should be treated as a hard bounce, not be retried and removed immediately from the mailing list after the first occurrence.

552 1 Requested mail action aborted, mailbox not found

The bounce message refers to a non existing recipient. Such recipients should be treated as a hard bounce, not be retried and removed immediately from the mailing list after the first occurrence.

554 30 Sorry, your message to *@yahoo.com cannot be delivered. This mailbox is disabled (554.30).

This indicates that you’re sending to an inactive mailbox. Hitting a high number of such mailboxes indicates bad list quality.

554 Message not allowed - [PH01] Email not accepted for policy reasons. Please visit https://postmaster.yahooinc.com/error-codes

This indicates a permanent failure triggered by DMARC failure, Spamhaus listings or various other Yahoo policies that prevent your emails from being delivered.

554 5.7.9 Message not accepted for policy reasons. See https://postmaster.yahooinc.com/error-codes

The above error occurs when emails are not properly authenticated or headers are incorrectly formatted. We've seen such bounces when special characters in the Subject line header are not properly encoded.

553 5.7.2 [TSS09] All messages from xx.xx.xx.xx will be permanently deferred; Retrying will NOT succeed. See https://postmaster.yahooinc.com/error-codes

smtp;553 5.7.2 [TSS11] All messages from xx.xx.xx.xxx will be permanently deferred; Retrying will NOT succeed. See https://postmaster.yahooinc.com/error-codes

This indicates that Yahoo permanently blocked your sending IP/domain. You should first find out why this happened, mitigate the issue on your end and then try to get unblocked by reaching out to Yahoo support.