Deliverability: Technical configuration checklist

Server security

The servers you use to send your emails should generally have adequate external technical security so that third parties cannot unexpectedly send spam via your mail servers. Is there a firewall, for example? Are the servers constantly monitored? Is the server not configured as an Open Relay? ...

Check: The servers you use to send your emails should be under the sole and full control of your email service provider to prevent misuse by third parties.

Sending process

Standard-compliant sending: The structure of each email and email delivery should comply with applicable technical standards, i.e. they should in particular be RFC compliant.

Resource-saving sending: The sending of emails should be as resource-efficient as possible for the receiving mail servers. Some major email service providers (such as Microsoft Outlook) have set limits on the number of connections that can be opened at the same time. Find out whether your shipping service provider is adjusting the shipping speed accordingly.

Separated mail streams: Sending marketing communication separately on the one hand and transactional or service communication on the other hand can be beneficial for deliverability. Use different IP addresses and sender domains for different types of communication. In this way, contacts who have unsubscribed from your marketing communication, for example, won't be confused by the fact that they continue to receive transactional emails from the same sender — which may even end up in the spam folder. Email providers such as Gmail, Yahoo and AOL have explicitly included the separate sending of different types of communication in their guidelines for mass senders.

Sender authentication

Identifiable, static, and dedicated IP addresses: The IP addresses used to send your marketing emails should in any case be able to be clearly assigned to your shipping service provider and the mail server used — e.g. via the so-called Whois entry. Using a so-called reverse DNS lookup, the receiving mail servers should be able to determine the associated domain for each IP address. Many shipping platforms also offer their customers so-called dedicated IP addresses. If your shipping service provider has assigned you as a company such a dedicated IP address, only your emails will be sent via this address. This allows you to work out good deliverability values for your IP without being affected by the shipments of other customers from your shipping service provider.

SPF: The Sender Policy Framework (SPF) is a process that is intended to prevent the sending of fake emails from your sender domain. For this purpose, a so-called SPF entry is stored on the server for the sender domain. It lists the IP addresses from which emails may be sent in the name of your sender domain. The receiving mail server can query the SPF record and thus check whether the emails it receives on behalf of your sender domain come from an authorized IP address. Together with the DKIM process, SPF is currently the most important authentication method for many large email providers. Therefore, make sure that a correct SPF record has been set up for your sender domain.

DKIM: DomainKeys Identified Mail (DKIM) is another method for sender authentication. Unlike SPF, DKIM uses a cryptographic method. The owner of the sender domain stores a so-called public key on his server — and provides each of his emails with a digital signature in the header. He can compare the signature and key and determine whether the two match or not. You can easily check whether your emails have a DKIM signature: View the complete header of your email and see if you can find a signature there.

DMARC: Protects domains from being used for email spoofing, phishing scams, etc. A DMARC record for the sending domain tells a receiving server whether or not to accept a message that purports to be from your domain. For this purpose, the Identifier Alignment is checked. Domain owners are informed if the shipping domain is misused.

Complaints & Unsubscribers

Abuse and complaint addresses: Despite best precautions, some of your recipients may complain to you about alleged spam or want to report misuse of your sender address. In this case, appropriate feedback channels must be available, including abuse or complaint email addresses. Some major email service providers — such as Yahoo and AOL — maintain their own feedback loops, which mass senders should sign up for. For CSA-certified senders, a field with the name “X-CSA Complaints” must also be integrated in the header area of each email, in which a CSA complaint e-mail address is noted.

Identifiable recipient lists: If there are complaints about your emails, make sure that you can reliably identify the problematic campaign in question and determine exactly which list of recipients the campaign was sent to. For this purpose, it is a good idea to insert a unique identifier in the header area of each email. CSA certified senders must therefore include a “List ID” field in the header of every email.

List-Unsubscribe: To comply with applicable legal requirements and avoid complaints, recipients of your marketing communication should be able to easily unsubscribe from the communication in every email. For this purpose, an unsubscribe link is usually integrated in the footer of every marketing email. For several years now, there has been an additional option: the so-called “List Unsubscribe”. For senders who support the list-unsubscribe method, a “List Unsubscribe” field can be found in the header area of every email. Either an HTTP link or an email address, or both, can be entered there. Recipients can unsubscribe from email communication by either contacting the specified email address or calling up the specified HTTP link — e.g. clicking on it or copying it into the browser. CSA certified senders are required (with exceptions) to include a list-unsubscribe field with an HTTP link in the header. Large email service providers, such as Gmail, automatically process the list-unsubscribe link in the header and offer their users special unsubscribe buttons in the user interface based on this link.