Email Deliverability Tips

Sasha Hanau | 22nd November 2017

Getting your pulse survey invites delivered

It’s notoriously hard to control emails and with so many factors affecting deliverability, it is often hard to pinpoint problems when they don’t land as expected in your recipient’s inbox.

What is ‘deliverability’?

‘Deliverability’ is the measure of success for your emails reaching the inbox without bouncing, or being marked as spam. Simply put, successful email deliverability is your message arriving in the inbox of the recipient as intended. If you have issues with high bounces, flagging spam filters or low engagement, you may have email deliverability issues.

Many factors that affect email delivery, like ISPs, MTAs, throttling, bounces, bulking, and spam issues. It’s a world full of horrid jargon words that baffle even the most tech-savvy individuals!

Technically speaking, delivery of emails is based on acceptance by the relay server (a.k.a. the recipient’s server which may often be your own internal servers if sending invitations to staff for example) to complete the function. Once the relay server has accepted the email for delivery there are a number of things that may prevent the email from reaching the recipient.

With a rising increase in email spam, ISPs have been forced to implement more stringent restrictions on delivery and filters to rule out spam traffic. This makes it increasingly difficult for them to effectively do their jobs without occasionally suspending a safe and legitimate email along the way. ISP filters do often rectify themselves (self-correct) but on other occasions, action from the sender is required to reverse any blocks.

What factors affect email deliverability?

Your deliverability primarily depends on your reputation with the ISPs who provide inboxes, such as Outlook, Yahoo, Gmail, Hotmail, etc. This “reputation” is the general level of trust granted by ISPs. ISPs can either help or hinder your ability to send email campaigns. This general reputation is a combination of two more specific reputations: those of your IP and your sender domain.

Read our resources article to find out more about The Happiness Index’s sending domains.

The factors affecting deliverability.

User complaints

When your recipients click on “mark as spam”, a complaint is recorded by ISPs and shared with our email partner. These complaints have a negative impact on our reputation. The maximum level of complaints tolerated by an ISP is 0.1%.

A high-level of hard bounces

A good reputation requires that only a small percentage of your emails “bounce” or get returned by the ISPs because the email account is no longer active (hard bounce) or the mailbox is temporarily full or the recipient is out-of-office (soft bounce).

ISPs rate the cleanliness of your email list by the volume of hard bounces. If your email sends out results in a significant volume of hard bounces, this may suggest your data is out of date or untoward in some way. High bounce rates make your email look like spam to an ISP and therefore your email may get held up.

Keeping your bounce rate low by implementing procedures to immediately remove email addresses that return “hard” bounce is essential.

Email content and infrastructure

This includes the HTML, copy, links included in and the subject line of your email. All have to be correct and non-spammy for maximum deliverability.

The receiving email providers’ availability

Sometimes deliverability is affected only by factors on the recipients’ end. The server to which it is being delivered must be available to receive the mail. Because email uses a store-and-forward protocol, a sending server will typically queue messages for a period of time when the receiving server is unavailable. In multi-server environments, the message might be delivered to a perimeter server, but if the recipient’s mailbox is unavailable (offline perhaps), the perimeter server can hold the message and deliver it later.

What you can do to improve email deliverability…

Preparing your email campaign

Be responsible with your data and keep it clean. When you upload people and email addresses to our system we are trusting that you have the permissions needed to email those people. Usually, this is pretty simple as your data will include your clients or employees who have usually opted in already via your contracts and other T&Cs. This is particularly important

If you are surveying event attendees or anyone with a private consumer email address (Gmail, Hotmail etc.) then you should be able to provide evidence of how they opted in. We cannot send invitations to email addresses that have not explicitly opted-in.

The quality of your data and the email addresses included is important. The better the data, the better the deliverability. The more opted-in or authority you have to email people on your list the less likely they are to make a complaint or mark the invite as junk.

If you do not know the origins of your email list then please do not upload it. Your email address list and its cleanliness affects our reputation and our account with our email provider can be closed should we accidentally hit a spam trap… Spam traps are fake email addresses released by ISPs to trap spammers. Hitting one means our IP may be blacklisted.

Avoid emailing free online and personal addresses

Sending to one of the free online email services like Gmail, Yahoo, MSN, etc. and personal email addresses is significantly more challenging with sending to business email addresses. Because they receive so much more traffic generally, their spam settings have to be tuned differently and this makes them more sensitive sometimes.

Personal email addresses also have more rules protecting their usage and extra care over privacy and permissions is key here.  The Happiness Index strongly recommends avoiding personal email addresses if possible. Their spam filters are notoriously hard to navigate and deliverability is typically lower than for other types of email address.

Message content counts – think like a spam filter

Message content is a major factor in determining how deliverable a message is. By examining the content of emails (including attachments, URLs, message text, and headers) email providers are sometimes able to identify potential spam or malware and will block suspect emails from being delivered. Each provider and organisation will have its own spam and filter settings so it’s best to check yours and whitelist IPs and specific sending domains like The Happiness Index’s at the outset.

Filtering technology now makes use of collaborative filters, where multiple sites and services can contribute spam reports to a centralised reporting service. The problem with collaborative filtering is that once one filter somewhere decides that a message is spam, other sites that consume the same filtering data will block it also. Filtering system algorithms are not often public so it can be hard to identify sometimes why you might have been unable to pass filters.

Check your copy for spam keywords

Make sure your subject line and body of email don’t include any keywords that can trigger spam alerts. Subject lines specifically are major spam indicators. Avoid spammy subject lines and be personal or inventive with your invitation subject lines – they affect open rates (and deliverability)!

  • Avoid ALL CAPITALS, excessive and unnecessary use of punctuation (!!!) and use symbols and SP$C!AL CH@RCT3RZ sparingly, and only when relevant.
  • Consider carefully your calls to action e.g. “urgent action” or “act fast” and “respond now”. These can appear spammy thanks to the retail world using them to advertise offers, promotions and sales.
  • Be concise – many email clients may truncate subject lines with too many characters. Be creative with your invite copy and make it clear what the email contains.
  • Avoid shortened URLs if possible as they are a notorious technique used by spammers to hide the nature of URLs they link to. Spam filters can block emails using shortened links even if they are legitimate. Also, avoid inserting the full URL link as text in the body of your email. Instead, create a hyperlink with the appropriate text, ensure all your links go to legitimate domains and are valid and functional.
  • Use images sparingly – A historic spam technique was to send emails that contain just one image, or many images and very little text in HTML emails in order to bypass spam filters that were based primarily on spam keywords. Spam filtering is now based much more on sending reputation than content though image to text ratio does still carry some weight with spam filters and is something you will want to be mindful of. Remember, many email clients or devices are not configured to display images by default. Always use ‘alt text’ behind your images so even if they don’t appear, your recipients will know what they were.
  • Properly format your email templates are important. We provide a selection of tried and tested templates for you to use, but there is nothing to stop you using your own email templates along with a generic link (settings permitting). Maybe your marketing department or agency is on hand to help? If so, that’s fine but we can’t help ensure your emails’ deliverability if you use your own third-party provider and code. The code has to be correct, and you must provide both a plain text and HTML version to help navigate spam filters. Design templates responsively so they are tablet and mobile-friendly.


Things to check/do before you send your emails.

Mark the sender as a ‘safe sender’ and whitelist our domain and IP address.

To ensure invites are not sent to junk folders please ask your IT team to white-label the domain you are sending emails from and the IP address or range in use.  This is essential to ensure emails sent from our system are not held up as suspicious, or spam email.

Sending multiple invitations over time for pulse surveys means it is advisable to tell your recipients to mark your email invites as a being from ‘Safe Sender’ so that future emails will be automatically flagged as safe content. To do this they can usually just right click on the initial email and mark as ‘safe’.

Minimise complaints – warn recipients not to mark your emails as ‘junk’ or ‘spam’

When recipients mark emails as junk or spam in their email provider it has an impact on the sender’s reputation. Ensure your recipients do not mark survey invites as junk or spam otherwise other emails internally may also be flagged and this will decrease the likelihood of your emails being delivered. Ensure your recipients are expecting the email and know what to do when they receive it.

Test, test, test your email invitations!

Ultimately the best way to see if your email provider or that of your recipients (if external) accepts and delivers your emails is to test it.

Conclusion – Multiple Internal & External Factors Affect Email Deliverability!

Sadly, emails can sometimes be unpredictable. Factors, both internal and external, (some within your/our control and some not) affect what percentage of your email invites can be delivered. The most important thing to do prior to sending out any email communication is check you have planned the campaign properly. Check each of the points above are fully optimised and contact your account manager if you are unsure about anything. Keep your data squeaky clean, and just bear in mind that emailing personal addresses is likely to throw up more challenges than sending to corporate, company-owned addresses.

Please visit our resources section for the full article on email deliverability, and more details on how we help improve email deliverability for our clients.