How are email delivery issues between AT&T and Yahoo related?

Marketer from Email Geeks explains that ATT handles the mail first then relays to Yahoo. So any ATT looking blocks (like DNSBL:RBL 521) are them and any other mail issues (like TSS04, spam, deferrals etc) are Yahoo.

Email marketer from Email Marketing Forum states that AT&T email is essentially a rebranded Yahoo service. So, any major changes to Yahoo's systems, like DMARC policies or anti-spam measures, will directly impact AT&T users.

Email marketer from EmailProviderReviews.com mentions that due to the partnership between AT&T and Yahoo, changes in Yahoo's email policies often affect AT&T email users as well, particularly regarding spam filtering and security protocols.

Email marketer from Quora shares that AT&T email is powered by Yahoo. So, problems with Yahoo's systems often cause issues for AT&T email users.

Email marketer from StackExchange notes that AT&T email accounts run on Yahoo's platform, but AT&T may implement its own specific rules, which sometimes cause discrepancies in email deliverability between AT&T and Yahoo domains.

Email marketer from Reddit explains that AT&T uses Yahoo's infrastructure for email. Therefore, issues on Yahoo's end can impact AT&T users, but AT&T also has its own filters that can cause independent delivery problems.

Marketer from Email Geeks shares that the MXes are ATT, but the mailbox UI is Yahoo. So if the mail is blocked at the gateway it's most likely an ATT issue, after that it's most likely Yahoo.

Email marketer from SenderScore Community points out that because AT&T leverages Yahoo's infrastructure, if Yahoo has widespread deliverability issues due to spam complaints or blacklisting, it's likely AT&T users will experience similar problems.

Email marketer from EmailGeeks suggests that while AT&T email is hosted by Yahoo, AT&T's own customer service and support protocols often differ, leading to different resolutions for users experiencing similar email issues on the two platforms.

Expert from Email Geeks explains that it’s complicated. They have their own set of filters, and having a problem at att.net does not necessarily mean that you have a problem at other yahoo domains, but problems at yahoo domains often affect att.net.

Expert from Word to the Wise explains that historically, AT&T outsourced their email platform to Yahoo. This means that many email delivery issues stem from Yahoo's infrastructure or policies, which directly impact AT&T users. However, AT&T also has some of its own filtering mechanisms, so issues may arise independently as well.

Documentation from RFC-Editor details SPF and DKIM standards and explains that email infrastructure providers who share resources, such as Yahoo and ATT, must ensure that mail authentication is properly configured to ensure messages are properly authenticated, which in turn, should enhance deliverability.

Documentation from Yahoo Small Business Help notes that while AT&T accounts are hosted on Yahoo's infrastructure, AT&T may have specific policies that influence email deliverability independently of Yahoo's general policies.

Documentation from AT&T Support explains that because AT&T uses Yahoo's email platform, certain outages or systemic issues on Yahoo's side will invariably affect AT&T email services. However, AT&T also manages its own customer service and billing which can create separate issues.

Documentation from Postmastery's knowledge base explains that AT&T using Yahoo's infrastructure means email authentication (SPF, DKIM, DMARC) configurations must align with Yahoo's policies to ensure successful delivery to AT&T inboxes.

Documentation from DMARC Analyzer Knowledge Base indicates that due to the partnership, DMARC policy updates on Yahoo's end can affect AT&T email users, requiring senders to comply with Yahoo's authentication requirements to ensure deliverability to AT&T addresses.