Why Is My Newsletter Going to the Spam Folder or Not Being Delivered?

There are many different factors, both in terms of the technical setup of your email and its content, that may result in your email newsletter landing in the spam folder, or not being delivered at all.

There are many different criteria that influence the delivery so it may end up in spam. The delivery is mainly influenced by the recipient or his provider. The providers use certain rules according to which they check the newsletter and decide whether it's spam or not. If a mailing does not comply with these rules, the newsletter will be blocked (hard bounce) or not forwarded to the recipient (not delivered).

Basic spam filter techniques

• Header Filter (also known as Reputation Filter): Ensures that the e-mail header has not been manipulated and comes from a safe source.
• IP Filter: This is an important step in filtering the header. The filter is based on the IP reputation. If an IP address is on a blacklist, the newsletter will be intercepted here.
• Sender Filter: Uses internal measures to decide if the sender is reliable.
• Content Filter: Checks if the content of the email is suspicious. This usually includes the Bayes classifier method.
• Word Filter: Checks whether the email contains current and known fraud vocabulary.
• URL Filter: Identifies links within the email that are currently being used in widespread phishing campaigns or that could be suspicious.

More complex spam filter techniques

• Rule-based filtering: Works with custom rules to rate emails for statistical matching and content. For example SpamAssassin, an open-source filter, works this way. The user sets specific thresholds for the spam filtering, which define what spam is, what spam could be, and what is not considered spam. Emails with lower spam values end up in the inbox. The user decides how low they have to be in order for the emails to end up in the inbox. 
• Fingerprint Filters: Works with specific message identifiers compared to other messages with similar identifiers. This solution was developed by CloudMark.

In general you should avoid the following things to pass spam filters

• The subject and the sender/response name consist only of uppercase letters, contain special characters or emojis.
• The campaign doesn't include an unsubscribe link 
• The content or subject uses terms that are intended to be typical spam words. Our system is based on public blacklists, which can vary.
• Subject has been written completely HIGH POST
• Use of a non-existent sender address
• Bad image-text-ratio. Don't use only pictures, make sure there is enough text to create a good balance. A good ratio is 2: 3.

Optimize your campaign:

• Provide your audience with relevant and interesting information. This can make your recipients mark or save your address. The ISPs will recognize these settings as a sign of high-quality content. That alone can keep your emails out of the spam folder.
• We also recommend storing a sender ID and DKIM entry. This reduces spam bounces and that your campaign is assigned as spam and additionally increases the delivery rate.