MARKETER'S FIELD GUIDE - GMAIL - Validity
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MARKETER’S
FIELD GUIDE
TO
GMAIL OUTLOOK YAHOO
Table of Contents
Gmail 4 Outlook.com 11 Yahoo Mail 19
Spam Filtering 4 Spam Filtering 11 Spam Filtering 19
Postmaster Services 5 Postmaster Services 13 Postmaster Services 20
Email Infrastructure 6 Email Infrastructure 14 Email Infrastructure 20
Partners 7 Partners 15 Partners 21
Whitelists and Prioritized Delivery 7 Whitelists and Prioritized Delivery 15 Prioritized Delivery 21
Gmail Inbox Categories 7 User Interface 15 User Interface 22
Unsubscribe Methods 9 Message Features 16
Unsubscribe Methods 17
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 2 returnpath.com
Introduction
Thanks to better ways of filtering and blocking spam,
inboxes are nearly free of unwanted mail—but not
without a price. On average, 20 percent of global
permission based email never reaches its intended
destination—your customers’ inboxes.
While it would be great if there was a single algorithm
that all of the mailbox providers used, that simply isn’t
the case. Gmail, Outlook.com, and Yahoo Mail have
each developed unique spam filtering formulas to
deliver the email their users want and protect them
from malicious messages.
In this guide, we’ll clear up misunderstandings about
the different rules of deliverability, and help senders
understand what it takes to reach inboxes at the top
three mailbox providers.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 3 returnpath.com
Gmail
Google’s free email service, Gmail, launched in 2004 and in just 13 years has become the world’s largest webmail service
provider. Currently, Gmail has over a billion active users.
As the top webmail provider, understanding how to reach Gmail inboxes is crucial for senders. However, the requirements
for reaching Gmail inboxes are a closely guarded secret. Unlike many of its large competitors, Gmail doesn’t utilize
whitelists, disclose use of public blacklists, or provide a lot of direction, tools, or support for senders.
In this section, we will talk about Gmail’s known spam filtering practices, their recommendations for email infrastructure,
and their postmaster services. We will also provide some recommendations to help senders navigate the path to the
Gmail inbox.
Spam Filtering
Gmail primarily uses its community of users to determine whether email is spam or not. Gmail considers the following user
feedback important in their spam filtering decisions:
Spam reports/complaints Starred messages
Not spam votes Messages replied to
Messages read and deleted Inbox activity
Messages deleted without reading
Content
As with most spam filters, the content of the email headers, body, and attachments is scoured for keywords, images, HTML,
URLs, malware, and many other common components. Content is always included in the overall spam filtering algorithm,
but how much weight it carries usually depends on the reputation of the sender.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 4 returnpath.com
Gmail continued
Sending history Blacklists
Gmail temporarily blocks new IP addresses without a Gmail does not make any blacklists available publicly. However,
reputation for the first two to 24 hours, then delivers small our research shows a correlation between spam filtering at
amounts of mail to both the inbox and the spam folders to Gmail and Spamhaus.
gauge subscriber reactions. If complaints are too high, future
emails will be delivered mostly to spam. If more people rescue Postmaster Services
messages from the spam folder by clicking “this is not spam”
Previously, Gmail was very secretive about their policies
during this period, it indicates that the mail is safe to be
around reaching the inbox. But in 2015 they launched their own
delivered to the inbox.
postmaster site to provide senders with some insight about
what it takes to reach Gmail users.
Engagement
User engagement is a major factor in Gmail’s filtering
Gmail postmaster tools
decisions. Gmail evaluates both a user’s engagement with
To begin using the Gmail’s postmaster tools, senders need
their mailbox in general and their engagement with a specific
to first add and verify their authenticated domain. Once
sending domain to determine what to deliver to each user.
authenticated, senders need to prove they own the domain
Users who interact with email from a domain regularly are
by entering the DNS TXT or the DNS CNAME. Once verified,
more likely to get those messages placed in their inbox.
senders will be able to access several dashboards.
Additionally, users who frequently interact with their mailbox
overall receive a higher percentage of messages in their inbox
Bulk sender guidelines
than other users.
Gmail compiled a list of best practices for reaching Gmail
users in their Bulk Sender Guidelines. This includes
It’s important for senders understand the relationship between
recommendations around subscribing new addresses,
these two measures of engagement. Users who are less
authentication, unsubscribing, and email format to help
engaged with your domain than with the rest of their mailbox
senders optimize their program to reach Gmail inboxes.
may have fewer of your messages delivered to the inbox, even
if you consider them an engaged subscriber.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 5 returnpath.com
Gmail continued
Feedback loop Email Infrastructure
Gmail’s feedback loop works a bit differently than a typical
feedback loop. Traditionally, when a user clicks the “report When it comes to proper email setup, Gmail advises the
spam” button, a message is sent back to the sender or to the following:
sender’s email service provider in Abuse Reporting Format
1 1. Consistently send from the same IP address(es).
(ARF) which shows the actual email address of the complainer
2 2. Have valid rDNS for sending IP addresses pointing to your
to be removed.
domain.
3 3. Use a consistent “From:” domain for each type of email.
Gmail, however, does not send feedback in the form of an
4 4. Sign messages with DKIM.
ARF. Instead, they use aggregated spam statistics to show
55. Publish a SPF record.
complaints overall by customers. In order to get information
6 6. Publish a DMARC policy.
in the postmaster tools for the feedback loop, senders need
to embed a header called the Feedback-ID, consisting of
parameters that uniquely identify their individual campaigns. Authentication
Gmail has increased their reliance on authentication. In
addition to authentication’s impact on filtering, Gmail
Header format: Feedback-ID: a:b:c:SenderID
distinguishes authenticated versus unauthenticated mail for
their users. If a Gmail user receives a message that was not
Feedback-ID is the name of the header to be embedded,
authenticated with either SPF (Sender Policy Framework) or
while a, b, and c are optional fields that can be used by
DKIM (DomainKeys Identified Mail), the sender’s profile photo
the sender to embed up to three identifiers (campaign/
or avatar is replaced with a red question mark.
customer/other).
SenderID is a mandatory unique identifier (5-15 characters)
chosen by the sender. It should be consistent across the
mail stream.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 6 returnpath.comGmail continued
In addition to authentication, Gmail also advocates Gmail Inbox Categories
Transport Layer Security (TLS) encryption. If Gmail receives
email not encrypted with TLS, they will display a broken lock To help Gmail users organize and quickly access their email,
icon in the message as a warning to Gmail users that the Gmail created an inbox filing system called inbox categories.
message is unsecured. All incoming mail is filtered into the following categories:
Social Social notifications and updates
Promotions Email marketing promotions and offers
Transactional emails like receipts and
Updates
shipping notifications
Forums Mailing lists and groups
Personal emails and messages from other
Primary
categories where the tab isn’t turned on
Partners
Although Gmail does not have any official partners, they do have
thousands of hosted business domains that use Google Apps.
Whitelists and Prioritized Delivery
Gmail does not offer their own whitelisting services, nor do
they subscribe to any third party whitelists.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 7 returnpath.comGmail continued
Gmail classifies incoming messages into these categories Gmail users have many options for influencing how messages
using a special algorithm that looks at everything from are categorized:
content and metadata to user feedback, then places them
into the relevant tab. Gmail currently enables the Primary, 1 1. Right clicking and selecting the desired category from the
Social, and Promotions tabs by default, but users can also “Move to tab” menu
choose to enable any combination of tabs or restore a single,
uncategorized inbox. For more information on how subscribers 2 2. Selecting the message and choosing a label from the
are currently interacting with Gmail’s categorized inbox, read dropdown
The Email Marketer’s Guide to Gmail Categories.
3 3. Starring a message: The starred message will appear in
the Primary inbox, but only that particular message will
appear in the Primary inbox. Future promotional
messages will still be filtered to the Promotions, Social,
Updates, or Forums tab.
4 4. Dragging and dropping a message into a different
tab: When a user drags and drops a message into a
different tab, Gmail displays a prompt asking users if
they would like all future messages from that sender to go
to the selected tab. If yes is selected, all messages from
that sender will automatically be sent to the new tab
going forward. Otherwise messages from that sender will
continue to go to the original tab.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 8 returnpath.comGmail continued
While helpful for Gmail users, Gmail’s multiple “inboxes” adds an extra challenge for senders attempting to reach their Gmail
subscribers. Similar to the way a message delivered to the spam folder typically goes unnoticed, messages not delivered to
the location subscribers expect won’t be seen or interacted with. As a sender, it’s important to ensure your emails are being
classified correctly as either Social, Promotions, Updates, or Forums. A misclassified email can result in lower open rates and
cause a bad user experience.
Following are suggestions from Gmail to help ensure your messages are directed to the correct category:
• Send different categories of mail (e.g., promotions, transaction notifications, social updates) from different,
authenticated sender addresses, and try to keep those addresses consistent over time.
• Avoid mixing different types of content in one email, since each message can only be sorted to a single category. For
example, putting a promotion into a transactional email may cause the message to be misclassified as a promotion.
Unsubscribe Methods
In addition to the unsubscribe links included in the email body, Gmail offers two different unsubscribe methods: an optional
List-Unsubscribe that senders can include and the report spam and unsubscribe button in Gmail’s user interface.
List-Unsubscribe
List-Unsubscribe is text located within a header that email senders can include to provide a safe way for end users to
unsubscribe. Many senders incorporate this text into their header as a way to dissuade subscribers from marking their email
as spam.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 9 returnpath.comGmail continued
After clicking the unsubscribe link, the following is displayed:
Report spam and unsubscribe
This method is triggered when a user clicks on the report spam button in Gmail’s user interface. When clicked, the user receives
the notification shown below, and is able to choose if they want to unsubscribe in addition to reporting the message as spam.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 10 returnpath.comOutlook.com
Launched in 1996 as Hotmail, Microsoft’s email service was one of the first web based email services. In fact, the name
original name Hotmail is a play on HTML, or HoTMaiL.
In 2013, Microsoft rebranded its service as Outlook.com to align with its desktop offering, Microsoft Outlook. Currently
Outlook.com has over 400 million active users and is available in more than 106 languages, making it one of the leading
global mailbox providers.
In this section, we will walk through Outlook.com’s spam filtering systems, features, support tools, and whitelisting services.
Spam Filtering
Exchange Online Protection
Exchange Online Protection (EOP) is a cloud based filtering system that protects Outlook.com users against spam and
malware. Microsoft is currently in the process of merging EOP and SmartScreen filters to increase the accuracy of their
filtering.
SmartScreen
Outlook.com utilizes Microsoft’s patented SmartScreen spam filtering technology. This technology uses a machine learning
approach to help protect users’ inboxes from junk email. SmartScreen technology learns from known spam and phishing
threats, as well as from Outlook.com’s customers who have chosen to participate in the Sender Reputation Data network.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 11 returnpath.comOutlook.com continued
Sender Reputation Data
Like many mailbox providers, Outlook.com factors volume, spam complaints, and spam traps into their filtering. However, the
company also relies heavily on their Sender Reputation Data (SRD) network for their filtering decisions.
Microsoft refers to their SRD program as the Spam Fighters Program. Along with other sources of reputation data—such as
the Junk eMail Reporting Program (JMRP)—SRD helps to train and improve the way their filtering classifies messages based
on email content and sender reputation.
The goal of the SRD program is to derive a better picture of a sender’s reputation by using feedback from trusted voters.
Participants in the SRD program are selected from active Outlook.com users at random from over 200 countries and no one
can volunteer for the program.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 12 returnpath.comOutlook.com continued
To get feedback, Microsoft resends copies of emails that members of their SRD panel received in the past 24 hours. The message
comes from Microsoft Spam Fighters and the sender’s original subject line is appended with “[Microsoft Spam Fighters] Junk or
Not?”. In the SRD email body, subscribers vote on whether they think the email is junk or not junk. A junk vote is seen as negative
feedback and a not junk vote is seen as positive.
SRD feedback is more reliable than feedback derived from complaints, because while senders can lower their overall complaint
rate by sending more volume, they cannot artificially lower SRD rates.
Postmaster Services
Smart Network Data Services (SNDS)
SNDS is a free service that provides aggregate data on email volume, subscriber complaints, spam traps, and more.
Result Example Verdict percentage
Green Spam < 10%
Yellow 10% < spam < 90%
Red Spam > 90%
SNDS uses a color coded system which indicates trustworthiness:
• Green indicates a positive sending reputation, and higher inbox placement rates to Outlook.com are likely.
• Yellow signals reputation issues starting to surface, and a mix of inbox and junk folder placement is likely.
• Red means that there are serious underlying reputation issues, which are causing most, if not all, emails sent to land in
the junk folder.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 13 returnpath.comOutlook.com continued
Junk Mail Reporting Program (JMRP)
Outlook.com offers their Junk eMail Reporting Program (JMRP) as a free feedback loop service to anyone who wants to
sign up. JMRP reports are generated as the result of spam complaints originating from Outlook.com users only, and does
not include SRD participants. The headers of the received complaint will also indicate if the subscriber marked it as junk
or phishing. Emails marked as phishing indicate that the sending identity wasn’t known, or perhaps something in the
content looked suspicious.
Support
Outlook.com offers self help and escalation paths for senders having deliverability issues. Senders are asked to ensure
they are following all best practices on the Outlook.com troubleshooting page. If senders are certain they are following
best practices, they can enter a ticket to the postmaster team.
Email Infrastructure
Outlook.com asks that senders’ mail infrastructure comply with the following:
• SPF: Outlook.com asks all senders publish an SPF record for the return-path.
• DKIM: Outlook.com also conducts DomainKeys Identified Mail (DKIM) checks on inbound email.
• DMARC: Outlook.com recommends senders publish a DMARC record to reject or quarantine mail sent from
illegitimate senders.
• DNS: Outlook.com requires a valid reverse DNS with a fully qualified domain name (FQDN). If Microsoft webmail
domains are unreachable, Microsoft recommends querying the most current list of MTAs through nslookup:
“nslookup –q=mx hotmail.com”
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 14 returnpath.comOutlook.com continued
Partners
Outlook.com does not currently have any partners.
Whitelists and Prioritized Delivery
Outlook.com does not maintain an internal proprietary whitelist. They do however participate in Return Path’s Certification
Program. Return Path Certification provides preferential treatment to accredited senders, allowing them to bypass certain filters
to reach the inbox. Those accepted into the Certification program are required to maintain the standards set by Return Path and
its participating partners.
User Interface
The Outlook.com interface makes it easy to sort through personal mail, social notifications, graymail, and more.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 15 returnpath.comOutlook.com continued
Message Features
Scheduled cleanup
Scheduled cleanup allows users to set rules to automatically delete
old emails and only keep the latest from a sender. For most senders,
this isn’t an issue. But for senders that send multiple times a day, a
different From: addresses for each mail stream may be needed.
Categorization
Outlook.com’s categorization can be used as Quick Views for users,
which is a similar concept to Gmail’s tabbed inbox.
Archive
Outlook.com’s archive feature moves all messages to the Archive
folder keeping the main inbox clutter free.
Delete all from
The “delete all from” functionality allows users to easily delete all
email from a particular sender based on the From: address. This is
good news for any business that has had to deal with Outlook.com
users using the “Report Junk” button in the past.
Focused Inbox
Outlook.com’s new feature separates the emails receive into
two inboxes. Emails users frequently interact with arrives in the
“focused inbox” with the rest delivered to the “other inbox.”
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 16 returnpath.comOutlook.com continued
Unsubscribe Methods
Like Gmail, Outlook.com also takes advantage of the List-Unsubscribe header. There are two ways subscribers access the List-
Unsubscribe functionality: through the “too many newsletters” footer or the “sweep” feature.
Too many newsletters? Unsubscribe.
As shown below, Outlook.com displays the “Too many newsletters?” verbiage under the email. It is important to note that this
verbiage is not part of the email. Rather, it’s part of Outlook.com’s user interface. When the hyperlink is clicked, the following
popup will be displayed if a List-Unsubscribe header is present.
If the List-Unsubscribe header is not included, the following popup will be displayed:
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 17 returnpath.comOutlook.com continued
Sweep unsubscribe
Using Outlook.com’s Sweep feature, users can select With either method of unsubscribing, the user will see a
one of several actions for a given email, including screen like this where they can click a button to confirm
unsubscribe. the unsubscribe.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 18 returnpath.comYahoo Mail
Yahoo Mail was one of the first free webmail providers to hit the market and is one of the three largest providers in the world with
225 million users. In June 2017, Yahoo was bought out by Verizon Communications, which in 2015 also bought AOL. Verizon has
not yet disclosed any plans to merge Yahoo Mail with other email services.
In this section, we will look at Yahoo Mail’s filtering process, services, and offerings for senders.
Spam Filtering
Yahoo builds the majority of their spam algorithms in house. They put a heavy emphasis on content, URL filtering, and spam
complaints from users.
Reputation
Yahoo is one of the few mailbox providers that filter email based on the reputation of both the sending domain and the IP
address. So reputation is critical in determining inbox or bulk folder placement. Reputation is driven by many factors including
unknown user rates, spam complaints, and spam traps.
Engagement
Engagement has always been an important measure of subscriber interest for senders, Yahoo is now placing greater emphasis
on engagement as part of their filtering decisions, as well. Factors being considered include:
What messages What messages are moved How quickly mail
are opened between folders is deleted
To reach Yahoo inboxes, it’s important to send relevant email that your subscribers want. You can determine what resonates
with your subscribers by tracking opens, clicks, and conversions along with other hidden engagement metrics.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 19 returnpath.comYahoo Mail continued
Postmaster Services
Yahoo tells senders the best way to get delivered to the inbox is to avoid looking like a spammer. Visit their postmaster page to
troubleshoot Yahoo delivery issues and make sure you are following their recommended best practices.
Troubleshooting SMTP errors
If your mail isn’t getting delivered to Yahoo, refer to your SMTP log. Once the bounce code is discovered, review Yahoo’s list of
common SMTP errors to determine the reason for the error.
Complaint feedback loop
Yahoo offers a complaint feedback loop (CFL) service. We recommend that you suppress users who complain immediately to maintain
a positive reputation with Yahoo. Note that DomainKeys or DKIM authentication and access to the postmaster@DKIMdomain
mailbox to submit verification key are required to sign up for Yahoo’s CFL.
Email Infrastructure
SPF, DKIM, and DMARC
Authenticating email with SPF and DKIM is recommended. Yahoo! supports DMARC and the standards that are required.
Connection and throughput
Servers should be configured to allow for 150 simultaneous connections with throughput set at 20 emails per connection. Rate
limiting will occur for high complaints and poor reputation, so use this as a guideline to determine your optimal setting.
rDNS
Publish a PTR record for your sending IP addresses, and use a Fully Qualified Domain Name (FQDN) so it doesn’t look like a
dynamically assigned IP address is sending mail.
Use a consistent and static “From:” address
Senders using consistent domains and sending From: addresses benefit when subscribers whitelist their email address. It also
helps prevent email campaigns being identified as spam by Yahoo’s spam filters.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 20 returnpath.comYahoo Mail continued
Partners
Yahoo has several partners including AT&T (which include BellSouth, SBC, and Ameritech), TNZ, ExtraNZ, and Nokia. These
partners utilize Yahoo’s infrastructure for their customers’ email. Each partner has its own filtering at the gateways before mail
is handed over to be processed by Yahoo’s filters, but we have found email sent to these partners should have inbox placements
rates that are consistent with direct Yahoo users.
Prioritized Delivery
There are two kinds of priority listings: Yahoo’s internal Bulk Sender Application and Return Path Certification.
Internal Bulk Sender Application: Return Path Certification
Yahoo’s Bulk Sender Application is free, and allows Yahoo also honors the Return Path Certification
senders to submit their IP addresses for review. Based program. Return Path Certification provides
on the review, Yahoo may alter the sender’s reputation preferential treatment to accredited senders,
for increased inbox placement. Those accepted are still allowing them to bypass certain filters to reach the
subject to certain filters including user level filtering, inbox. Those accepted into the Certification program
content filtering, and URL filtering, and inbox placement is are required to maintain the standards set by Return
not guaranteed. Path and its participating partners.
While the exact criteria for increased placement isn’t public,
Yahoo does require a positive sending reputation. New IP
addresses—for example, when you move to a new email
service provider or add a new IP address—must be in
service at least 30 days before Yahoo will evaluate them for
Bulk Sender status.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 21 returnpath.comYahoo Mail continued
Yahoo User Interface
Yahoo’s user interface makes it easy to interact with email and access additional Yahoo applications.
Marketer’s Field Guide to Gmail, Outlook, and Yahoo 22 returnpath.comGet to Know Return Path
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Marketer’s Field Guide to Gmail, Outlook, and Yahoo 23 returnpath.comBusinesses run better and grow faster with Boston – Corporate Headquarters
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