Deliverability is a moving target, and identifying why your message doesn't reach the inbox isn't always clear. The goal of this guide is to help illustrate how specific ISPs handle incoming mail, and share how messages can be optimized for better deliverability. If you are having difficulty with deliverability to all ISPs, you may want to take a look at sender reputation best practices and check out how your ESP protects deliverability. Before a message is delivered, the ISP must determine a) if the sender is legitimate, b) where the message should be placed, and c) if the recipient wants to receive the message. Each ISP has a different approach to inbox placement, filtering, whitelisting, and handling recipient actions.
Scroll to the bottom of this post to view the Deliverability Troubleshooting Guide Slideshare.
"Even if you have a reputable sending history, users can vote your email as spam and affect your overall reputation. So, if you want to get your emails to the inbox, the best practice is to send relevant content to the users who want it and have opted to receive it." Yahoo Mail deliverability FAQs
Yahoo has a complex anti-spam filtering system that works to stop unwanted email before it reaches the inbox. Knowing how Yahoo handles incoming email can help improve your deliverability. For example, continuously sending email to users who are not engaged, or who mark messages as "spam", will hurt your delivery metrics and sender reputation.
IP address reputation
Autonomous System Number (ASN) reputation
DomainKeys Identified Mail (DKIM) signatures
While Yahoo does not have a whitelisting program, they do allow bulk senders to submit IP addresses for review. This may help your deliverability at Yahoo, but it isn't a guarantee of inbox placement.
Yes, and they highly recommend taking advantage of it. Signup for Yahoo's feedback loop.
Send email only to those who want it.
Make sure subscribers have actively verified their intent to receive your mailings.
Honor the frequency of the list's intent. Don't start sending daily emails to subscribers of your monthly mailing.
Honor unsubscribe requests quickly.
This can happen for several reasons. Yahoo may not be filtering your emails to the spam folder, but they can be placed there by the recipient. If a user blocks your domain, the user preferences will override anything that the anti-spam filter decides. If you notice your emails are regularly being sent to spam, Yahoo urges you to review your sending practices.
There can be multiple reasons your email did not reach the inbox. Make sure you check your sending domain and email address as well as the email content and links within the email to help improve your chances.
"Shared email services can have multiple domains using one IP to send email. If the same IPs are sending unsolicited commercial email, and your presumably valid email, then your reputation can be impacted." Bulk email industry standards and best practices
Opt out users that have marked your email as spam in the past.
Use separate IPs depending on the email's content.
Submit your IPs for review.
Make sure your emails are DKIM Signed.
Control your email traffic, spread out your campaign over a period of time.
Check your email content, especially your subject line.
Publish reverse DNS (PTR) records for your sending IPs.
Enroll in Yahoo's feedback loop.
Separate your mail streams by IP address and domain.
Review SMTP reply codes often.
Be CAN-SPAM and DMARC compliant.
Consider sending a reconfirmation email to inactive subscribers periodically. Or just remove them entirely.
Your SMTP servers should identify the originating IP address of the email and indicate this in the email headers to help you diagnose spam problems.
Read more about Yahoo Mail's deliverability best practices here.
"Mail classifications depend heavily on reports from users. Gmail users can mark and unmark messages as spam, and can move non-spam messages between inbox tabs. In both cases Gmail learns from user corrections and over time automatically adjusts the classification to match users’ preferences." Bulk Senders Guidelines, Gmail
When sending email to Gmail, you need to keep in mind that this inbox is slightly different than the rest. In addition to anti-spam filters, Gmail organizes the inbox based on categories such as promotional, social, and transactional. Gmail has filters setup to determine which category an email belongs in, as well as relying on user feedback. Gmail users can easily mark an email as spam or not spam, and move emails between categories. Gmail works hard to get legitimate senders to the inbox, but it is possible for your emails to be wrongly placed in the spam folder. Users have the ability to mark a message as “not spam”. Gmail will listen to user feedback and automatically correct problems in their filtering process. If the user does not consider your mail as spam, you should have no problem getting into the inbox.
Gmail provides additional best practices for sending bulk email to Gmail users. Following these suggestions will help prevent deliverability issues.
The 'From:' address is listed in the user's Contacts list.
A user clicks 'Not Spam' to alert Gmail that messages sent from that address are solicited.
No, Gmail relies heavily on user actions to determine inbox placement.
No, Gmail relies heavily on user actions to determine inbox placement.
Only email users that have opted in through an email asking to subscribe to your list.
Only email users that have opted in to your list by manually checking a box on a web form, or within a piece of software.
Do not use an email address list purchased from a third-party.
Subscribing all users by default is not considered an acceptable opt-in. For example, setting a checkbox on a web form or within a piece of software and requiring users to explicitly opt-out of mailings.
Make sure the recipient can unsubscribe from your list by:
A visible link in the body of the email, allowing users to easily unsubscribe.
By replying to your email with an unsubscribe request.
Because Gmail can help users automatically unsubscribe from your email, they strongly recommend providing a 'List-Unsubscribe' header which points to an email address or a URL where the user can unsubscribe easily from future mailings. (Note: This is not a substitute method for unsubscribing.)
Gmail inbox categories classify emails into different categories to help Gmail users organize their mailboxes. Gmail will filter and place your emails into these categories automatically. Users can also choose to have specific emails or senders placed in a specific the category. To ensure your messages get placed in the correct category, Gmail suggests:
Separate emails by category and send individual emails for each category. For example, a promotional message should be sent as a separate email than a transactional message.
Try not to mix different content categories. Don’t put promotional content into a notification or transactional email, or all future emails may be mis-categorized and placed in the wrong inbox folder automatically. For Gmail, it is better to send two separate messages to the same address than a single message with promotional and transactional information.
Affiliate marketing programs are set up to reward a 3rd party for bringing visitors to your site. At times, this can be a target for spammers and can cause harm to your sender reputation. Gmail wants those using affiliate programs to keep two things in mind:
If your brand becomes associated with affiliate marketing spam, it can affect the mail sent by you and your other affiliates.
It is your responsibility to monitor your affiliates and remove them if they send spam.
Use a consistent IP address to send bulk mail.
Keep valid reverse DNS records for the IP address(es) from which you send mail, and ensure they are pointing to your domain.
Use the same address in the 'From:' header on every bulk mail you send.
Sign messages with DKIM. Gmail does not authenticate messages signed with keys using fewer than 1024 bits.
Publish an SPF record.
Publish a DMARC policy.
Automatically unsubscribe any emails that have bounced multiple times.
Periodically send confirmation messages to users.
Include a list of all the mailing lists the user is signed up for, and give them the ability to unsubscribe.
Gmail recommends that you verify each email address before subscribing them to your list.
Don’t put promotional content into a notification or transactional email. This will prevent messages from being mis-categorized in the Gmail inbox.
Read more about Gmail's deliverability best practices here.
"Each IP that delivers mail to AOL has a reputation -- roughly good, bad, or somewhere in between. Your reputation is a holistic view of your IP and takes into account a wide variety of factors including -- but not limited to -- spam complaints, this-is-not-spam reports, spam folder deliveries, and invalid recipients." IP Reputation, the Whitelist, and Inbox Delivery at AOL
If you find yourself having trouble making it to the inboxes of your AOL subscribers, the first thing they recommend is looking at your IP reputation. Making sure you have a good sender reputation is vitally important when sending to AOL (as well as other ISPs.)
Having a high number of invalid subscribers will harm your reputation. AOL recommends you keep the number of invalid subscribers as low as possible because these will hurt your IP reputation. Find out how many of your subscribers are invalid here.
Have a good IP reputation
Get on the AOL whitelist
Yes. If you are having difficulty delivering email to AOL, a feedback loop (FBL) would benefit you. AOL will send you a copy of each complaint generated when an AOL member reports your email as spam. You can use this information to remove complainers from your mailing list. Signup for AOL's feedback loop.
Yes. The standard AOL whitelist offers protection from certain spam filters. Being on the whitelist is in no way a guarantee of inbox delivery. IPs on the whitelist can still be spam foldered, temporarily deferred, temporarily blocked, or permanently blocked if they have a bad reputation. AOL whitelist programs are designed to help AOL work with organizations and individuals who send solicited bulk email while simultaneously protecting their members from unwanted email.
The Enhanced White List (EWL) delivers mail to the inbox with links & embedded images enabled, and is only available to senders that are already on the standard whitelist. All IPs on the standard whitelist are evaluated for the EWL daily, and inclusion in the EWL is granted and rescinded automatically based on the sending IP's reputation.
Make sure you are only sending to those that have specifically requested to be on your mailing list.
AOL prefers that you double opt-in your users, so make sure they are true subscribers.
Be clear and let the subscriber know upfront what to expect, how many emails, how often, and what type.
Users should not have to log into a website to be able to unsubscribe.
Make your unsubscribe process obvious.
Then make it easy for the user to unsubscribe, like a one-click unsubscribe web page.
Verify Connecting IP.
Perform a manual SMTP telnet test.
Confirming DNS Resolution Ability.
Verify your system's ability to resolve AOL's name-servers.
Verifying your IP's reverse DNS.
Review our SMTP Error Messages.
Ensure your IP is not an open relay.
If you are still having trouble, you can submit a support request to AOL.
Make sure you are only sending to those that have specifically requested to be on your mailing list.
Have DKIM set up to authenticate your emails, and ensure consistent reputation across your domain.
Send your emails from a consistent email address.
Ask subscribers to add your email address to their address book. This will help your email get placed in the inbox of that user, and have images and links enabled.
Segregate IPs - Do not send your marketing emails from the same IP you use to send user email, transactional email, or alerts.
Make your unsubscribe process easy.
Remove those who unsubscribe immediately.
Have an active FBL on each one of the IPs you are using.
Remove subscribers that mark your email as spam.
Read more about AOL's deliverability best practices here.
"We track a sender’s reputation using various mechanisms, such as IP and domain reputations, content checks, and user feedback. Then we make our filtering decisions." Postmaster information for iCloud Mail
iCloud puts an emphasis on senders following best practices to get their emails into the inbox. Your email will be filtered based on your IP reputation, content, and user activity. They encourage senders to review their list and limit their sending only to confirmed, engaged recipients. iCloud may have a stricter definition of what it means to opt in and be engaged than what you have been following for your list. Knowing how iCloud views this and other best practices will help you deliver emails more successfully.
There is no whitelisting program with iCloud. They rely on several mechanisms to determine how to filter incoming email. iCloud tracks IP and domain reputation, content checks, and user feedback to make a decision on where to place the email.
iCloud does not offer a feedback loop service. They urge senders to closely manage their lists, and only send to engaged subscribers that have shown that they want to keep receiving your emails.
Periodically suppress inactive or disengaged subscribers from your mailing list.
Remove addresses that bounce consistently.
Honor unsubscribe requests as soon as possible.
iCloud Mail will automatically detect and block junk mail before it reaches the inbox. They work to keep legitimate emails going to the inbox, but mistakes can and do happen at times. iCloud urges customers to review and follow best practices when sending bulk email. This will help to avoid filters classifying the email as junk mail.
When iCloud refuses a SMTP transaction the mail server will generate a report on the error. You can check your mail logs to find more information. Most errors will also include a URL that provides more information.
If you have followed all the best practices suggested by iCloud, and have reviewed the error messages from your mail logs, but still can’t determine the delivery issue, you can contact their postmaster team for more information.
You can send an email to firstname.lastname@example.org, and make sure to include the following information:
Your company name
Your email domain
The IP addresses of the affected mail servers
The SMTP errors that you're getting from iCloud mail servers
A detailed description of the issue, including when it started
Send only to those that have subscribed to your emails, no list rentals or purchased lists.
Make it easy for the user to unsubscribe.
Make your emails RFC 5322 compliant.
Segment your marketing and transactional emails, but use consistent sending IPs and domains.
Use a consistent 'From:' name and address to clearly identify your brand.
Use Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) to authenticate your emails.
Track SMTP errors, both temporary and permanent, and take the appropriate action.
Implement a policy to handle email addresses that have bounced.
Periodically remove inactive subscribers from your list.
Don't reactivate email addresses that are on your unsubscribe or suppression list.
Read more about iCloud's deliverability best practices here.
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