Email Marketing ISP Guidance:

Email Marketing ISP Guide


The key mission of Yahoo is to deliver messages that people want to receive and filter messages they don’t. With Yahoo, you’ll need to perform list management tasks frequently and monitor hard & soft bounces as well as inactive subscribers.

Sending email to users who aren’t reading them or who mark them as “spam”, will hurt your delivery metrics and reputation. Send email only to those who want it. Use an opt-in method of subscription for your mailing list and make sure subscribers have verified their intent to receive your mailings. Review email content for common characteristics of spam. Test your emails’ visual look with image placeholders. Many of your recipients won’t see images in your email. Email on Acid is an excellent place you can go to check your message rendering. Make sure you are linking to domains, not IP addresses. Yahoo will filter out these links.

Don’t include: HTML forms, JavaScript, or embedded objects (like flash or ActiveX.) Yahoo uses two server side configurations and will count these objects/forms against your reputation. Have separate IPs depending on your email content type. Shared email services can have multiple domains using one IP to send email. If the same IPs are sending unsolicited commercial email and your reputation goes down, Yahoo will hope on the wagon and filter your messages from that IP.

Secure your mail servers and update your software with the latest security patches. Filter user-generated content before sending it, to prevent spammers from using your resources. If your servers act as “open proxies” or “open relays,” spammers may attempt to send their own mail from your systems. At a minimum, your SMTP servers should identify the originating IP addresses from the email and mention this in the email headers to help you diagnose spam problems.

Use bulk mail authentication best practices and review SMTP reply codes often. If your messages are being blocked, look closely at any SMTP error codes your mail servers are returning. Make sure you’re addressing the root of the problem.

Bulk Mail Authentication Best Practices

      • Don’t retry 5xx messages – Retrying permanent errors increases the chances your mail will be de-prioritized.
      • Retry 4xx messages – This is a temporary error.
      • Enroll in the feedback loop – If you’re signing your emails with DKIM or DomainKeys

A feedback loop analysis can help you track and manage your spam complaint rates. Always make sure your emails include DKIM authenticated signatures. Check if you’re DKIM signing the email. DKIM signature helps Yahoo authenticate that email is safe, secure and from the senders who claim to send it. Not being DKIM signed makes your emails appear to be sent by a spammer.

Publish reverse DNS (PTR) records for your sending IPs. Yahoo is more likely to downgrade an IP’s sending reputation if there’s no reverse DNS entry for your IP address or your mailing IP looks like a dynamically-assigned IP instead of a static mail server.

Yahoo Will Downgrade Your Reputation if

      • There’s no reverse DNS entry for your IP address
      • Your mailing IP looks like a dynamically-assigned IP instead of a static mail server.

Be CAN-SPAM and DMARC compliant. Invalid DMARC records can cause problems if you’re sending from non-compliant bulk mailing services.

What Yahoo Looks for

      • Perform list management often
      • Send email only to those who want it
      • Review email content for common characteristics of spam
      • Separate your mail streams by IP address and domain
      • Secure your mail servers
      • Review SMTP reply codes often
      • Emails include DKIM authentication signatures
      • Publish reverse DNS (PTR) records for your sending IP’s
      • Be CAN-SPAM and DMARC compliant



Deliverability to is based on your reputation. Microsoft releases reputation data via its Smart Network Data Service (SNDS) program. Windows Live Hotmail uses SPF and DKIM authentication. They filter email using Symantec/Brightmail Probe Network, Smartscreen filtering, and other content-level filtering. Blocking may result from being listed with Brightmail; removing those blocks requires contacting Symantec, not Hotmail. The Smart Network Data Service (SNDS) gives you the data you need to understand and improve your reputation. The SNDS gives you the data you need to understand and improve your reputation at Microsoft. Data includes filtering, complaint rate, and spam trap hits.

What Microsoft Looks for

      • Sending reputation
      • They release reputation data via SNDS
      • DKIM and DMARC authentication
      • They filter using Symantec/Brightmail Probe Network, Smartscreen filtering, and other proprietary content-level filtering
      • Being listed with Brightmail, may block you.



AOL focuses heavily on DKIM authentication and references the block lists maintained at The Spamhaus Project. Their spam filter is proprietary and custom-built. Metrics such as; complaints, unknown users, content, bounce processing, and spam traps influence AOL’s inbox placement.  If you need to view your reputation, find detailed bounce information, or open a ticket with the postmaster, AOL offers a postmaster site.

What AOL Looks for

      • DKIM Authentication
      • Spamhaus References
      • Proprietary & customer-built
      • Complaints
      • Unknown Users
      • Content
      • Bounce processing
      • Spam traps



What does Gmail look for when processing inbox placement? One is it’s double opt-in/confirmed opt-in history. This is when someone signs up for emails and then has to verify that their information is correct. Therefore it’s a great idea to have an “add to address book” section or any confirming CTA that a recipient will click on in the first email. This button helps you pass spam filters a lot faster because it is similar to a personal whitelist for the user.

Gmail focuses heavily on recipient engagement. Therefore keeping list hygiene is important. If you are sending to old lists, your engagement will be lowered and gmail will count that against you. Avoid URL shorteners, such as bitly. However there are URL shorteners that esps provide which are fine to use.

Use a list-unsubscribe link in the header. Gmail also looks for DKIM authentication and is leading the charge for DMARC with Microsoft.  Gmail has a postmaster tools website where you can view the reputation of your IPs and Domains.

What Gmail Looks for

    • Double opt-in or confirmed opt-in
    • Recipient engagement: click-throughs, starring messages, moving emails into folders
    • List hygiene
    • Avoid URL shorteners
    • Use a list-unsubscribe header
    • DKIM and DMARC authentication
    • Use sub-domains
    • Their classifier (spam filter) checks the WHOIS for domain registration.  If it’s hidden, it knocks your trust level way down.


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