Email deliverability can be a complex issue that involves a multitude of different factors. Success in this field requires changing one’s perspective – instead of seeing only the sender’s side, one must also consider the recipient’s view. 


Although a lot has been written about this topic, many marketers and senders still hold the following beliefs:

  • The more emails sent, the higher the response will be
  • As long as I have a legal opt-in I can send what I want and ISPs have to deliver.

Unfortunately, this point of view does not reflect reality and shows only one side of email marketing.

For those familar with the concept of sender reputation and recipient (re)actions – which are the basis of the fomer – this advice will be a reminder. For those unfamiliar with these concepts, it should serve as guidelines for how to perform successful email marketing – by sending relevant emails to users who appreciate them.

Try to think like an ISP
All businesses need to keep their users or customers happy. Cluttering their inboxes will have ISP users switch to other ISPs which provide better filtering. However, false positives must also be avoided. An incorrect categorization of wanted emails as spam will have the same effect as filling the inbox with UBE/UCE. All major ISPs are constantly adding more criteria in order to determine which emails are actually wanted and which are not. In recent years providers have done a really good job in this area. ‘Cheating’ ISPs, so that they deliver large amounts of unwanted emails, has become virtually impossible.

ISPs search for factors in their customers’ behaviour to determine if they want the email messages you are sending. Positive reactions to your messages (among which are opens, flagging emails as important and many more) improve your sender reputation. Almost all actions which can be performed in a recipient’s mail account are used to weigh your reputation, either in a positive or negative way.

Remember: your recipients are ISP customers! ISPs will always want to make them happy, rather than a sender, even of legitimate emails. And: It is not possible to ‘force’ recipients to want your emails.

Put yourself in the recipient’s shoes
In order to determine how your subscribers will react to your emails and, subsequently, how ISPs will treat your emails, Emarsys recommends running through your entire registration/subscription process and observe it from a recipient’s point of view. Register for your own services. Do you receive a confirmation email for your subscription, or even a double opt-in email asking you to confirm your registration? If you were the recipient, which process would you trust more? Are the services you offer sufficiently disclosed, i.e. is it clear to recipients what they will receive? What do recipients expect of your services, offers or newsletters? And do you change your sender name and sender address frequently?

Frequency and timing matter. Monday, Thursday and Friday are usually the most popular days for sending commercial emails. Email frequency varies among different business types. Coupon or daily deal marketers are mostly high volume senders, with approx. 5 emails a week, while others send the same amount in a month. What works for one may not work for others. If your email frequency is too high, subscribers will turn away from your services; they will delete your emails immediately, unsubscribe, or report your emails as spam. All these reactions have a major impact on deliverability.

Compare the results for different frequencies, even if you already offer various intervals for your services on the subscription page or the user preferences page. Users and recipients who are engaged with a brand will accept a higher frequency. We recommend a separation of actives with high(er) sending frequency from less actives (moderate frequency) and inactives, who should only receive the occasional reactivation mail (e.g. once a month – these mails should constitute a maximum of 5% of your total daily volume to minimize negative impact on your reputation while making sure contacts are not completely lost).

Expectations matter. Sending messages which your recipients are not expecting can reduce your list size, as contacts are more likely to unsubscribe; this will also hurt your reputation and deliverability, due to a higher complaint rate or just plain inactivity. The more relevant your messages are, the higher your open/click rates and your sending reputation will be.

Major ISPs like Gmail, Yahoo and Hotmail have highly sophisticated mechanisms in place which help them to find out – based on recipient behaviour – if messages are wanted or not. They cannot be tricked – irrelevant emails cannot be successful. How can the relevancy of one’s emails be increased?

  • Send a welcome message to newly registered users or, even better, use a ‘double opt-in’. Start your relationship with recipients immediately after their registration. Welcome messages should include the registration details and detailed information on the services you offer (FAQ, privacy policy, other channels, etc). Use this opportunity to collect even more information on your users.
  • Send only those messages of which you have informed the subscriber. Your contacts expect to receive what they subscribed to, nothing else.
  • Use the behavioural data you have gathered from your users, and target based on user profiles.
  • Send personalized messages. A personalized greeting line is the absolute minimum; in general, all content sections should be checked, and if possible, be tailored to individual recipients.

Similar to relevancy, consistency is essential, as it prevents users from cancelling your services and keeps your emails recognisable. Users add the sender addresses of wanted newsletters and services to their address book, as this enables the automatic display of images in new emails of the same sender. Changing your ‘From’ address can reduce your open rate drastically, at least for a while, and is not recommended. If you have no choice, we advise you to inform your recipients before you change the sender, and to ask them to add the new sender to their address book.

The content/design and branding of your messages as well as other webservices (website, landing pages, social media, etc.) must be consistent and recognisable. If recipients do not recognise the messages they are receiving as the service to which they have subscribed, this might trigger a negative reaction and, subsequently, have ISPs downgrade your level of reputation.

For more information on deliverability, please contact your Emarsys Account Manager.