Suppression lists

What are suppression lists and what are they used for

Suppression lists, or lists of unreachable addresses, serve as a means of maintaining your sender reputation and nurturing your subscribers. By using them, you suppress messages to certain addresses which, if sent, would be likely to do you harm. Our service will automatically filter out the email addresses found in these lists.

An email address may be suppressed for a variety of reasons. It may be syntactically invalid; the mailbox owner may unsubscribe from your mailings or issue a complaint; or the receiving server may be known to block certain types of emails it deems unwanted.

How does an email address become suppressed

Generally, there are three entities that may be the source of information used to render an address as suppressed:

The system: an address may be considered unreachable when a large number of delivery attempts fail. Other possible reasons include the address being registered as a spam trap.
The owner: your subscriber may cancel their subscription or issue a complaint.
The client: you may opt to add an address to a list with an appropriate status – unsubscribed, complainer, etc.

The particular source is returned as a value of the source field when calling the suppression/get API method. This method also provides the related cause – user complaint, unsubscription, delivery issues, etc.

Types of suppression lists in UniOne

There are two types of suppression lists in UniOne:

The global suppression list – addresses that are considered unreachable for all users. The only sources here are the system and the address owner, but never any of our clients.
The local suppression list contains addresses that are suppressed for your mailings only, based on previous sending attempts or the owner’s actions.

The global suppression list is a major benefit as it suppresses any mailings to addresses that are already known to be unreachable and thus helps you maintain a good deliverability score and solid sender reputation.

How suppression lists improve your deliverability

Let’s consider the following three scenarios.

Sending out marketing emails

Mass marketing emails are more likely to be considered as spam by mailbox providers, thus the primary goal is to avoid sending emails to unreachable addresses and keep the number of complaints to a minimum. It makes perfect sense to use our prior knowledge about the addresses that cannot be reached or whose owners tend to place complaints. As such, both local and global suppression lists are used for this type of email, which helps you achieve a good sender reputation and keep the number of complaints to a minimum, which in turn will improve your deliverability rate.

The default parameters for the email/send API method are optimized for this type of email.

Sending regular transactional messages

Abandoned cart emails, balance notifications, billing reminders and the like are anticipated by the recipient, so complaints are far less likely. In this case, it would be reasonable to turn off the global suppression list and use only the local one.

To use this scenario, set the bypass_global parameter value to 1 when calling the email/send

Sending high priority transactional messages

This category includes emails that need to be delivered even at the risk of degrading your sender reputation, e. g. account confirmations, password resets or security notifications. It would make sense to skip checks for both the global and local suppression lists. However, it is advised to consider possible cases where the local list needs to be used partially, for example, to suppress letters to known complainers.

In order to send high priority letters to addresses known to be unreachable, specify bypass_global=1 and bypass_unavailable=1. If you also need to contact unsubscribed addresses, add bypass_unsubscribed=1. Similarly, with bypass_complained=1 emails will be sent to complainers as well.

Managing suppression lists

To view, add or remove addresses from suppression lists, our Web API offers a set of suppression methods. For individual addresses, you may also use the Tools/Email search page in your account.<

You may remove addresses from your local suppression list whenever you like, however removal from global lists is limited to a few addresses per day and may not be available for certain addresses.

If you implement your own unsubscribing mechanism, we strongly recommend adding unsubscribed addresses to the UniOne suppression list as well, using suppression/set API method – this will help us to ensure that no emails are sent to anyone who has canceled their subscription. This is especially useful if your messages originate from several sources, and lists of unsubscribed addresses for different types of mailings are maintained separately.