There can be several reasons why emails are not delivered. For example, (intended) e-mails from our formats are incorrectly recognized as spam/junk by a spam filter of the receiving mail server or the mail client used and moved to the corresponding subfolder of the mailbox or blocked completely.

Note

If you were unable to resolve the issue with the help of this article and contact us, we will need the email address concerned in order to troubleshoot the issue. If emails from the formats have also been incorrectly classified as spam, please also forward a selection of these emails to us as an attachment so that we can investigate them.

It would also be helpful if you could provide us directly with the name of a technical contact from your company if the affected mail server is your own.

A not uncommon reason for the non-delivery of emails is a typing error in the email address used for the recipient. As web browsers nowadays support form entries, it can also happen that they automatically fill in an email address that has been entered incorrectly in the past and the user overlooks this before sending the form.

As an email service provider, we use Mailgun and Inxmail to achieve a better rating in the email servers' spam filters and thus counteract false recognition. For such service providers, ensuring the delivery of emails is part of their day-to-day business. In addition, if you define your own sender address for the emails (FROM header) from your formats, we set the so-called technical sender of the email (SENDER header) to an address from our domain portfolio. In accordance with RFC 5322, the SPF record defined for our Internet domain (see below for an explanation) ensures that the servers of the contracted service providers are authorized to send emails for contentbird GmbH. This also has a positive impact on the rating.

Recognition as spam/junk can be facilitated by the use of individual keywords within the email or by its structure (e.g. many images with little text). Likewise, links that are used with a different link as a caption can be seen as an attempt to defraud and lower the rating of the email. Avoid this at all costs. In addition, modern mail clients warn the user with a corresponding dialog when such a link is used. Contr

There can be many reasons why an e-mail is blocked. Typing errors in the recipient address are often the cause. However, there are also technical measures to prevent the distribution of spam or the unauthorized sending of messages in the name of an Internet domain/company. Such a configuration is "best practice" and we recommend that you also configure this for your Internet domains. In this way, you ensure that user confidence in your brand is maintained, as the recipient will not receive any emails that have been distributed by unauthorized sender servers.

Changes discussed in the following paragraphs should only be implemented by experienced administrators, as incorrect configuration can restrict or completely prevent the sending (or delivery) of messages from your Internet domains. contentbird GmbH cannot accept any warranty or liability for this. Therefore, please check changes several times before activating them. The individual paragraphs list external test platforms for the various configuration options as an aid, which can at least check the correct setup. Then test the dispatch and delivery from the corresponding domain.

The brands and services listed belong to their respective owners and are only used to illustrate connections or as a useful example of the use of an option.

As the term "DNS" is often used in the following, we would like to explain what it is at this point:

The Domain Name Service (DNS), as the name suggests, takes care of the conversion of (speaking) Internet addresses (domain names) to IP addresses. In addition, the DNS directory of an internet domain can also be used to provide a wide range of information regarding the responsible email servers for this internet domain or, for example, to verify the domain ownership for services such as Google Analytics.

The sender policy framework uses entries in the DNS of an Internet domain to identify the email servers that are authorized to send emails for this domain. For example, the Internet domain contentbird.io defines that emails of the form @contentbird.io may only be sent via servers of contentbird GmbH or third parties commissioned by it. Email servers that now check an incoming email first determine the so-called SPF record of the sender domain. If this is defined, a comparison is made to see whether the sender server matches the defined list. If this comparison fails, the incoming e-mail is usually rejected. In accordance with RFC 5322, the SENDER header (technical sender of an e-mail) has priority over the FROM header (the "logical" and visible sender of the e-mail) that is normally used for this check. We make use of this to identify ourselves technically correctly as the technical sender in emails sent from our formats for your company with an email address from one of your domains in the FROM header and to ensure a positive check of the sending email servers.

You can have the SPF record for any domains checked for structural errors on the following page, for example: https://www.spf-record.de/spf-lookup/

With DKIM, every outgoing e-mail from an Internet domain is provided with a digital signature, which ensures that the e-mail can only come from a mail server that is under the control of the owner of this domain. In order to be able to check the signature, the public part of a key pair is stored in the DNS of the Internet domain. Email servers that now check an incoming email first determine the so-called DKIM record of the sender domain if the email contains a DKIM signature. If this is defined, the system checks whether the signature created with the private (non-public part of the key pair) key can be verified with the public key part. This ensures that a signed e-mail actually comes from the designated Internet domain.

However, no statement can be made if there is no signature in the e-mail. However, it would at least be an indication of spam if the domain defines a DKIM record but the email does not use it.

contentbird.io, for example, defines DKIM records both for its own mail servers and for external service providers via which emails are sent for the formats played out.

t-online.de is planning an enormous tightening of the authentication of incoming emails from the beginning of the 3rd quarter of 2021 and requires that all emails must be signed in compliance with DMARC using DKIM. If you don't act, you risk delivery problems at t-online.de and probably in the long term also other providers.

We are currently examining how we can deal with this situation and what measures we can take for you and to what extent you as our customers will have to make configuration adjustments.

DMARC is the most powerful tool to ensure that emails in your name actually come from you. DMARC combines the Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) to provide comprehensive protection for outgoing emails by specifying how SPF and DKIM must be checked and how to proceed in the event of a failed match. Unfortunately, DMARC ignores the SENDER header specified by RFC 5322 (the technical sender of an email, if specified) and only compares the FROM header (logical sender of an email) with the SPF record.

You can check whether you are using DMARC on a domain, for example, on the following page: https://www.dmarcanalyzer.com/de/dmarc-de/dmarc-record-check/

If you use DMARC on your Internet domain, e-mails sent by us on your behalf will most likely be rejected by many receiving servers if you do not include the sending servers used by us in the SPF record of the corresponding Internet domain!

You must now take action, as contentbird has no further influence on this.

You currently have several options:

In addition to the SPF, DKIM and DMARC techniques presented above, other filter mechanisms can of course be used on mail servers. However, only the IT department responsible for the server can answer and check questions about this.