Email Deliverability: Key Components To A Good Sender Score

There are key components that contribute to good email deliverability (and similarly, a good sender score), which is a must for any company looking to regularly send content to current and potential customers!

But, how do you make sure you have a strong sender score and your emails continue hitting people’s inboxes – and not the junk folder?

Here’s eight items to examine. Want more? Try our free email marketing basics course!

1. List quality, regular maintenance, and hygiene

Keeping your list clear of bounces and regularly removing inactive subscribers reduces the appearance of being a spammer. A clean list is comprised of regularly emailed, active subscribers who have not bounced, unsubscribed and are routinely engaging in your marketing emails. ISPs look suspiciously on email senders who have a high volume of unknown recipients, inactive recipients and regularly send to bounced email addresses.

Bounces fall into two categories: soft bounces and hard bounces.

  • Hard bounces are email addresses that are invalid, closed or non-existent, these are permanently invalid.
  • Soft bounces are email addresses that are active but the email is turned away prior to delivery, this is temporary problem.

Soft bounces are more nuanced than hard bounces, the data returned to the sender contains reason codes, which should be mined for information and processed accordingly. A full list of server reason codes can be found here, although not all codes listed are applicable to email directly but email bounce codes can be found in the list starting with 5xx.

It is highly recommended that senders build a programmatic approach to handling soft bounces. This should include logic that parses the bounce codes differently based on what the status code is relaying.

List quality also helps avoid the pitfalls of spam traps and blacklists. While no list is immune to these it is a significantly smaller risk when you maintain a fully permissioned opt-in list that is regularly purged of inactive and invalid data.

2. Spam Traps

A spam trap is an email address that was typically not ever intended for communication but purely intended to lure spam. In order to prevent legitimate email form being invited the email address is typically only published in a location hidden from view but visible to email address harvesters (which are illegal under CAN-SPAM). Since no email is solicited by the owner of this address any messages are considered to be unsolicited and therefore spam.

3. Blacklists and Filters

There are five major types of blacklists and filters.

  • Third Party/Public Blacklists: Companies that publish publicly available databases of bad senders. No special credentials are required to start a blacklist but some are more popular than others and are actually used as references for ISPs and some corporate IT departments.
  • Sever-side filters: These are filters such as SpamAssassin or Brightmail, they use their own sets of filtering rules to catch messages suspected of being spam. Some of these technologies use heuristics, Bayesian analysts and collaborative filtering. Many ISPs rely on customized server-side filters to filter messages. These filters may also take message volume into account and block a sender who exceeds a set transmission rate.
  • Client-side filters: Recipients know that spam can make it through the various processes in place to block it and therefore can utilize tools such as Norton AntiSpam, McAfee SpamKiller or even rules built into their Outlook client to filter messages.
  • Corporate blacklists: Software filters and hardware tools are available to email administrators that provide them the ability to create an internal blacklist and therefor block email originating from any organization for any reason for any length of time.
  • Private blacklists: Large providers like Gmail (Google) and Outlook (Microsoft) are likely to maintain their own proprietary list of known spammers and problem senders. Some provide feedback loops that give senders warning they are in violation of spam rules at the ISP and some (like Gmail) provide no feedback at all.

Deliverability testing through tools provided by your marketing automation platform or third-party services such as Litmus offer the opportunity to test emails for filtering prior to sending, thus giving a sender the opportunity to make changes before their message gets sent to the junk folder or not delivered at all.

4. Complaint rate

Even with a fully opted-in list and a very clean database complaints happen, recipients may hit the spam button when fatigued with your message (instead of unsubscribing) or might accidentally hit it.   Regardless of the way it happens, the email provider will still count this as a complaint.

It’s generally accepted that anything greater than 1-3 complaints per thousand (0.1%-0.3%) emails sent is enough to revoke whitelisting status on an IP address. Complaint rates beyond these are likely to result in negative hits to your sender reputation and deliverability.

As a rule of thumb, your complaints should never exceed your unsubscribes for a campaign, if it does, it should provoke research into the campaign and what might have caused the problem. Typically high complaint rates can be attributed to changes in your email programs, such as:

  • Changes in send times/dates
  • Frequency of messages
  • Content that a subscriber feels is not relevant
  • Using your list to promote third-party services/products or content your subscribers feel is questionable.

5. Email configuration

The technical configuration of your IP addresses and various domain and sender records are crucial to establishing your sender reputation. The infrastructure component of your sender reputation is measured by two key items: reverse DNS and host type. These items in conjunction with confirmed identity via SPF (Sender Policy Framework), SID (Sender ID), and DKIM (DomainKeys Identified Mail) ensure your email is properly configured to show your identity as a sender.  If you're wondering why your email deliverability and sender score have been negatively impacted, you need our primer guide!

Here is a baseline of the items to pay attention to when configuring your IP addresses for deliverability:

  • IP addresses should be static to build up your domain and IP address reputations consistently.
  • Senders who send more than 50,000 emails a week should maintain dedicated IP addresses (i.e. not utilize shared IP addresses pooled between multiple senders using a given Marketing Automation Platform or Email Automation Platform).
  • It is best practice to set up separate domains and subdomains for your marketing, transactional and corporate emails. Along these lines, it is highly recommended that the From address and domain actually match. Some ISPs are very picky about mis-matches in domain and from address.
  • Authenticate your IP/Domain with SPF, DKIM, DomainKeys and SenderID. Without these in place you are likely to end up in the junk folder (or not delivered at all).

In addition to the technical setup, consistency in your identity, from address, reply-to address and records (listed above) are critical to identifying yourself as a legitimate email sender and not a spammer.

6. Transmission rate, volume, and frequency

The rate at which you send emails out is important to ISPs. Spammers often send email without regard to volume, speed of send, or list cleanliness. To combat this, your ISP may sometimes perform a “volume block” (blocking transmission of massive amounts from one sender to many of their account holders) if they feel the volume of emails coming to them in the timeframe is excessive or potentially spammy.

It’s recommended that larger batches of emails be released in groups instead of a single “blast” – a good rule of thumb is to not force more than 40k emails per hour in any given send.

Frequency of sends is important in that you should keep a consistent frequency. If you have dips and spikes in your sending that are without pattern it is likely that you will appear to be a spammer to more stringent filters.

7. Content

Everything from the HTML coding and design of your email to the actual copy of the offer contribute to the content and are evaluated by filtering mechanisms (previously discussed under Blacklists and Filters and in Appendix: Spam Filters).   Everything from broken or mis-coded HTML to lack of a text-only version of your email, lack of alt-text for images or code embedded scripts in your HTML can cause a filter to block your messages.

Typically when discussing content, marketers associate using words like “FREE” or “ADVERTISING” to instantly doom their message to the spam filter. Unfortunately it’s not quite that simple as filters are much more nuanced and use a variety of methods to determine if a message is spam or legitimate.

The best possible results for avoiding content-based filtering is to test using a tool such as the deliverability tools in your marketing automation platform or a highly-regarded third-party source.

8. Gain Recipient Permission and Respect Their Preferences

Your audience falls into three buckets: new recipients, active recipients and inactive recipients, for each of these buckets you should have slightly different approaches.

New Recipients

  • Only send to those who have explicitly requested email from you.
  • Target “neutral” contacts (i.e., those who have neither opted in nor opted out) with the goal of gaining permission.

For this you will want to look at the specific legislation for the Regions/Countries you mail in, this is not always legal (ex: Canada).

Active Recipients

  •  Strengthen the relationship with active opt-in contacts by soliciting feedback on the quality and frequency of your communications, and their communication preferences. Confirm preferences with the recipient and then comply.
  • Send only what the subscriber signed up to receive.

Inactive Recipients

  • Re-engage inactive contacts by confirming subscription status one or two times per year.
  • Nurture inactive contacts and cut inactive contacts after they fail to re-engage after a set timeframe

And there you have it!

You’re now better-prepared to boost your email deliverability! You may also enjoy our Ultimate Marketing Resources Guide or our Resources Hub.

And if you ever need help with your email or marketing automation, don’t hesitate to let us help!

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