Yahoo! deliverability and best practices

Starting February 1, 2018, Oath (A Verizon company that owns both AOL and Yahoo!) began consolidating sending infrastructures between AOL and Yahoo!. This means that the AOL domains will continue to operate and accept email, but Yahoo! will handle spam filtering and processing.

You can get additional information about the changes and the impact here:

If you send email to AOL domains, we recommend that you follow best practices for both AOL and Yahoo! during this transition period.

Spam filtering factors

Yahoo! uses a combination of filtering technologies, reputation measures, whitelists, blacklists and other factors in its spam filtering formula. These include:

  • Spam filter technology
  • Complaints
  • Trusted users
  • Engagement
  • Reputation
  • Authentication
  • Whitelists
  • Blacklists

Spam filtering technology

Yahoo! uses a custom spam filter called SpamGuard. When a subscriber clicks the Report Spam button, the message is processed by Yahoo! SpamGuard. This filter learns to identify spam through user complaints. In addition, Yahoo! uses several methods to assist with engagement-based filtering.


Senders are expected to keep complaint rates below 0.2% for an IP address. If you have a deliverability issue at Yahoo!, you probably have a complaint rate higher than 0.2% and will need to lower your complaints to see improvement in inbox placement. Yahoo! Mail offers a free Complaint Feedback Loop (FBL) program to help email senders minimize complaint rates. If senders participate, Yahoo! Mail forwards complaints on emails sent from their organization that they can remove from their list and avoid continuing to send to those users and getting  more complaints from them.

Trusted users

Yahoo! has a set of trusted users whose complaints and This is Not Spam (TINS) markings are weighted more heavily than those of other users. Yahoo! uses trust as a multiplication factor in votes. Trusted votes outweigh normal votes and can swing complaint rates up or down. Originally, the trusted network was built of Yahoo! employees and their friends, but it has since expanded. It is not a volunteer role, so trusted users do not know they are trusted. The identities of trusted users are kept secret.


Yahoo! may also look at how your subscribers are engaging with the email you are sending. They may look at things such as deleting without reading or marking the email as spam (This is Spam, or TIS).

Yahoo! is also moving toward factoring the following user actions into its engagement filtering:

  • Immediate deletions, which indicates a level of unwanted mail because of the lack of interaction.


Reputation at Yahoo! is calculated for the following:

  • IP address reputation - This is the overall reputation of the sending IP address
  • URL reputation - All URLs within the campaign could play a part in your reputation at Yahoo!, whether these are domains in your control or third party such as tracking links. You should ensure that all URLs are not blacklisted on blacklists such as URIBL, SURBL or Spamhaus DBL
  • Domain reputation - Yahoo! Looks at the reputation of your sending domain and all sub domains that are part of it. They will look at historical data such as complaints and make decisions on your inbox placement.


Yahoo! uses Sender Policy Framework (SPF) and DKIM for authentication. Having DKIM implemented and working properly at all times is important because Yahoo! will not send complaint feedback loop messages when messages do not pass the DKIM check.

If using DMARC, ensure your record is valid as an invalid record can cause problems.


Return Path Certification is the whitelist Yahoo! Uses. IP addresses on the list receive an improvement in reputation and increased deliverability. Although there is an improvement in reputation, the email sent from the Certified IPs are still subject to content and URL level filtering.

Yahoo! internal bulk sender form

Yahoo! does not offer its own internal whitelist. However, it does have a program where high volume senders can submit their IP addresses for review.  Based on Yahoo!’s review, they will modify your IP’s reputation in their system if appropriate. IPs can be submitted for review here.

Yahoo! partner benefits

Yahoo! partners share whitelist benefits as well as FBLs. These include:


Yahoo! uses the following blacklists:

  • The Return Path Reputation Network blacklist (RNBL)
  • Spamhaus
  • Spam Uniform Resource Identifier Real-time Block List (SURBL)

Yahoo! deliverability best practices

The following is a summary of best practices for sending mail to Yahoo! members, including recommendations for inbox delivery, details about authentication, engagement, Yahoo!’s Complaint Feedback Loop and onboarding new IPs. Implementing these best practices will help improve your reputation, but they do not guarantee email delivery.

Important factors for inbox delivery at Yahoo! Include:

  • Spam complaints and user feedback, offered as This is Spam (TIS) and This is Not Spam (TINS) selection
  • Traffic and reputation history
  • Authentication
  • Content of the entire message, as well as bulk detection, URLs, and keywords
  • Engagement, based on subscribers moving mail from Bulk to the inbox. Yahoo! also includes other metrics in engagement performance, such as deleting without reading.

Recommendations for inbox delivery

  • Complaints and user feedback: Ensure you are signed up for Yahoo!’s Complaint Feedback Loop program and and are processing complaints. This will help you minimize complaint rates. Participants receive forwarded complaints from Yahoo! subscribers about emails sent from the sender's organization. This program helps senders to:
    • Understand what Yahoo! Mail subscribers think of their messages
    • Take corrective action to minimize the complaints generated by their mailings
    • Improve their sending reputation
  • Authentication: Make sure you are properly authenticating your email with DKIM and DMARC. Publish reverse DNS (rDNS) records for your IPs.
  • Engagement: Senders should ensure they are maintaining their list and removing inactive subscribers regularly. Consider removing or sending a re-confirmation email to inactive subscribers, as well as to subscribers who have not opened or clicked on emails for a while.
    • Segmentation: Target your subscribers with relevant content based on demographics and other attributes such as past purchase history, buying frequency, and industry.
    • Yahoo now caches images using a proxy server, so location based targeting may need to be adjusted. 
  • New IP addresses: Send only five messages per connection from new IP addresses (open a connection, send five messages, close the connection, then repeat).
  • Hosted accounts: Hosted email accounts, for example Internet service providers, universities, or other email hosting providers may experience delivery delays when sending to Yahoo! 
  • Message limitations: Yahoo! Mail accounts can send and receive emails up to 25 MB.

Yahoo Complaint Feedback Loop (CFL)

If senders participate, Yahoo! Mail forwards complaints about emails sent from their organization.

  • The verification code email sent by Yahoo when submitting the sign-up form is sent from:
  • Complaint Feedback Loop (CFL) reports are sent from and are DomainKeys Identified Mail (DKIM)-signed with

The Complaint Feedback Loop program supports both DomainKeys- and DKIM-signed email. Senders signing emails with either authentication technology who want to enroll in the program can visit the postmaster page to learn more or submit a Complaint Feedback Loop application to create and manage an account.

Yahoo! calculates the inbox complaint rate for Certified senders as the number of complaints divided by the number of emails delivered to the inbox. Yahoo! counts all complaints, but it weighs complaints differently in its reputation system (for example, if it sees one subscriber complaining about the same message repeatedly).


Make sure to sign your email with DKIM. It helps Yahoo to ensure your emails are safe and secure and that they are coming from you. Have a valid DMARC record to avoid any issues if you are sending from bulk mailing services that are not compliant. Also, without a reverse DNS record, Yahoo may downgrade your reputation because this may make it look like you are not sending from a static IP, but rather a dynamically-assigned IP.


Monitor bounces and track subscribers that are not opening or reading your email. Continuing to send to unknown users or inactive recipients with get your email deferred. Sending a re-engagement email to inactive subscribers periodically is a good strategy for identifying people to keep and remove from your list. Sending email to subscribers who are not engaged with your email, or who may mark it as spam, hurts your engagement metrics and reputation and ultimately results in poor deliverability.

Guidelines for establishing SMTP connections to Yahoo!

At Yahoo!, limit throughput to 20 messages per connection. If the 20 message limit is exceeded, the connection will be dropped without issuing an error message. There is no published limit to the number of concurrent connections, but Yahoo! asks senders to be respectful of resources and warns that resource hogs will be de-prioritized.

Domains and domain differences

There are some notable differences between some of the regional and hosted Yahoo! domains. It is beneficial to understand the differences when determining steps for troubleshooting delivery issues at  these domains.

  • Mailboxes hosted by Yahoo! (AT&T, Rogers, etc.): Gateway filtering occurs at the domain level. If senders receive a 4xx or 5xx error on mail to AT&T, these occur on AT&T's network. Once the mail makes it past AT&T's filters, it is sent to Yahoo! to be delivered to the subscriber's mailbox, where Yahoo! filtering occurs. The bulk vs. inbox determination is made by Yahoo! and Yahoo!'s reputation system applies.
  • Yahoo! Japan: Y! Japan operates like an entity that is separate from Y! Corporate. It runs its own mail platform, and while it leverages some of the same technology as Corporate, it has a custom implementation and a separate code installation. While it has access to all of the filters that the rest of the Y! global network employs, there may be local configurations that support differences or that override standard filtering to enable it to meet Japanese government regulations. There are separate mediation and support escalation paths for Y!JP, usually in Japanese.
  • Yahoo! China: Yahoo! China Mail suspended service as of August 19, 2013. All email and data were deleted. Subscribers had the option to migrate data to Aliyun Mail (, a service of the Alibaba Group. Mail sent to either or domains result in an smtp:550 relaying denied error.
  • Yahoo! South Korea: Yahoo! pulled out of South Korea entirely in December 2012.
  • Asia Pacific (APAC): In Asia, Yahoo! continues to operate in Hong Kong, Taiwan, and Japan. Yahoo! Taiwan has a separate postmaster.

Onboarding new IP addresses

There is no hard rule for volume at Yahoo!. However, Return Path suggests throttling email for one to two weeks to start gaining reputation.  

The best method is to send low amounts of email, gradually increasing the amount day after day until the Internet service provider sends a throttle code and increase the retry times. Monitor the SMTP codes generated by the Internet service provider. If the sender receives an error that indicates throttling, the sender should slow the volume and wait at least 24 hours before they resume mailing. Senders should:

  • Track the new IP address' progress with Inbox Monitor
  • Send mail to recent and active users who will be less likely to complain
  • Send low risk data and content that are not likely to generate complaints and are clean
  • Begin to add the new IP addresses to the existing whitelist once Internet service providers monitor volume
  • Ensure that bounce processing is in place prior to sending mail
  • Configure the system to handle the throughput that is acceptable for Internet service providers

Yahoo! bulk sender guidelines

Yahoo! Provides many more  recommendations for bulk mail senders and postmasters sending to Yahoo! Mail on its best practices page.

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