Email Deliverability

Delivered != Deliverability

Deliverability = Inboxing = Not getting sent to spam

"Delivered" happens when a message sent is accepted by a inbox provider's mail server. "Deliverability", or inboxing, is when a message sent has been placed in the recipient's inbox (in any of the tabs: primary, promotions or other) and not spam.

Why this is important

  • Email is almost always accepted by inbox provider's mail servers. It's common for delivery rates to be over 95%, even if a large portion of your mail is being delivered to the spam folder. Delivery rates give you false sense of security, especially when combined with the easily misunderstood industry jargon "deliverability".

  • During 2018, Slate was experiencing email deliverability challenges and rolled-out a series of options later that year that radically improved delivery rates. Newer clients have been urged to make these optional setup changes, but it seems like the request may have not made it to all older clients. These configuration options are available in most CRM systems, so this is not a Slate specific problem.

  • Throughout 2019, Google made a series of algorithm changes to aggressively combat spam and continues to fine tune. We have found that clients that are not actively managing their email reputation with Google eventually get caught up in filtering. Microsoft and Verizon Media Group have followed with similar and sometimes more aggressive changes. Setting up email authentication and aligning with your domain is the best way to improve and gain visibility into your email reputation with any inbox provider.

  • In 2020, COVID has caused unpredictable behavior by Google's spam filters and reputations to shift unexpectedly.

  • There has been a rise in filtering and scanning from safety and security bots. Companies like Gaggle ( and Barracuda Networks ( will open and click emails to determine if the contents are safe from inappropriate content and viruses before deciding if it will allow a message recipient to receive it. Unfortunately, this gives the illusion of high open and click rates and hides the reality that your messages are getting blocked. Slate's analytic systems do some of the work to filter out false positives from more well-known companies like Gaggle, but there could be instances where a similar competing technology is used instead.

Prior 2019, you could be a great email marketer without this arcane email knowledge. Today, you either need to learn or hire it.

We are mostly focused on Gmail deliverability

Most likely the majority of your potential student base is on some form of Gmail. We find that as Gmail deliverability improves, so does deliverability with other inbox providers. Our client averages for the US market are:

  • 60-65% of addresses are on a Google platform:

    • 40-50% use consumer Gmail

    • 10-15% are high school addresses on Gmail for Education

  • 10-15% are on a Microsoft platform, including consumer Outlook and Outlook 365.

  • 15-20% are on one of the remaining larger provider platforms: Verizon Media Group/Yahoo! /AOL, Apple's iCloud, Comcast, Charter, and Cox.

  • 5-10% are on a smaller provider's platform or in-house mail server

Email reputation model

Our typically email reputation management model is built on:

  1. Every day campus email as the foundation of reputation. This is a personal and highly engaged mail stream. Bulk mailing should be avoided from personal accounts. This mail stream should always have a high reputation: never-ever sends spams and is always wanted.

  2. Slate and other CRM systems are communicating with engaged recipients. This mail stream should generally be high reputation except when Gmail is testing new algorithms. This mail stream never intentionally* sends spam, but recipients' level of wanting to receive wanes over time. Unengaged recipients should be re-engaged or trimmed from lists periodically or risk unwanted email becoming spam.

  3. Waybetter is onboarding new prospects or re-engaging old in a highly managed mailstream. This mail stream never intentionally sends spams, but could be seen as unwanted as we attempt to separate the engaged, unengaged and unwanted. Reputation should be medium or higher, which is normal for a bulk mailer.

*Examples of when unintentionally spam can happen is: a typo in an email address (, a fake address ( or an old, unused email address is reused in a required field (

Baseline Definitions

  • Delivered = Messages accepted by mail servers / Messages sent. Most bulk sends have delivery rates between 96-99% and is not usually an import metric unless your rates are consistently below 96%.

  • Engagement Rates = (Number of messages opened + clicked + moved out of spam + filled from one tab to another + and more) / Messages sent. This rate is partially visible to senders through:

    • Click Through Rate (CTR) = Messages clicked / Messages accepted

    • Open Rate = (Messages that load images + clicked an email) / Messages accepted

    • Click to Open Rate (CTOR) = Messages clicked / Messages open

  • Conversion Rates = Goal complete / Message open. The goal should be a non-email related goals, a step removed from an email click and be bot resistant. Common examples include filled a form, watch half a video, scrolled to the bottom of a page, placed a deposit.

  • Spam Rate = (Messages rejected as spam + messages filtered + messages put into the spam folder + recipient flagged as spam) / Messages sent. This rate is only directly visible mailbox providers, but you get some indication of this from spam report rate (recipient flagged as spam/messages accepted)

  • Deliverability = 100% - Spam Rate

  • Authenticated: Email has been verified using SPF and/or DKIM

  • Aligned: Email has been authenticated under a school’s domain.

There are 3 primary reputation authentication tools

  • SPF: Tells mailbox providers a particular IP address/server is authorized to send email for a domain

  • DKIM: Tells mailbox providers this particular message has not been altered and was validated to come from a domain

  • DMARC:

    • Reporting: Allows mailbox providers to send XML reports to senders. These reports summarize who is sending on behalf of the domain and what authentication is being used, if any

    • Policy (optional): When a unauthenticated or unaligned message is sent, it tells mailbox providers to handle it normally (none), send to spam (quarantine), or do not accept it (reject). "Handle it normally" means follow the inbox provider's internal rules to determine if its spam. Authenticated and aligned messages are always set to handle normally.

Deliverability Reputation Sources

There are thousands of factors that determine

  1. Recipient's Personal History: How an individual recipient reacts to a mail source is the primary driver around reaching the inbox and will typically override an inbox provider other data sources

  2. Sender Domain (DKIM): Under authentication, this is the primary driver when there is not enough information at recipient level. Major mailbox providers (Gmail, Outlook and Yahoo) will attempt to construct synthetic domain reputation if you don’t set-up authentication.

  3. Sender IP address (SPF): While domain reputation has an increasing role in the determination of what is and isn’t spam, IP address still contributes a significant piece and plays a more important role when domain authentication isn’t set-up. If you have dedicated IP addresses, domain and IP addresses are strongly interacted, but less so when you use a shared service provider like Slate or MailChimp.

  4. Content: Content includes HTML code and hidden content, not just what is visible to the recipient. Major mailbox providers are increasingly using content fingerprinting and smaller mailbox providers continue to rules based (blacklist) methods. In addition, there are additional layers of content filters provided by safety and security companies like Gaggle and Barracuda. Content is usually not a primary driver, but has negative consequences if enough factors come together. Example: A Nigerian prince email will most likely go to spam no matter who is sending it. Here are some typical content filter:

    1. Network security gateway (like Barracuda): Typically work at an organization level look for potential security issues with all email coming in.

    2. Safety filters (like Gaggle): These system will typically screen the first few emails to the recipient from a new source. These filters will not block search emails, but will generate opens and click from bots

    3. Virus filters (like McAfee): Typically works at a device-level and will route email to the spam filter based on content rules

    4. Rule based scoring and filtering (blacklists): Works at mailstream and message level and creates spam score to determine if a message should be be blocked

    5. Content reputation (algorithmic fingerprinting): Works at mailstream and message level and uses algorithms to determine if a certain message is like messages that have been blocked, sent to spam or filtered to a specific tab

Positive Factors

Ranked to the best of our knowledge (i.e. only the Google knows)

  1. User whitelisting or filing - user adds you to an

    1. address book,

    2. never set to spam rule

    3. drags your email from promotions to the inbox

  2. Re-engagement - looks at an email several times

  3. Engagement - replies, opens and clicks, including clicking the unsubscribe link

  4. Sharing/Forwarding

  5. Long reputation history

  6. Consistent frequency and volume: daily, weekly, monthly and yearly

  7. Slowly ramping up traffic volumes

Neutral Factors

These could be positive or negative, it depends on how you are using them and how recipients react to them

  • Email content and images

  • Linked website reputation

  • Linked website Content

  • Age and length of the reputations

  • Email analytics (pixels, UTM parameters, click tracking)

  • Hidden content:

    1. HTML/CSS

    2. Preheader

    3. Email annotations

    4. JavaScript/AMP

Negative Factors

Ranked to the best of our knowledge (i.e. only the Google knows)

  1. Opens/Clicks and then marks as SPAM

  2. Marks as SPAM

  3. Being sent to SPAM

  4. Public link shorteners are well known potential security hazards

  5. Mismatched plain text domains to link domains (Your link text says visit "", but your link points to "")

  6. Flagged as

  7. SPAM Traps

    1. Pristine SPAM Trap Hits

    2. Recycled SPAM Trap Hits

    3. Typo SPAM Trap Hit

  8. Blacklists, both email and website

  9. Large, random traffic spikes