How does a spam filter work?
A spam filter is a program that runs on the mail client and server side. It checks all incoming messages and gives them a certain number of "spam points". If the score reaches a certain level, the message is automatically moved to the spam folder. These points are calculated according to a range of different criteria. Each spam filter, however, has its own rules. This explains why some e-mails arrive with some recipients and others' don't. But one thing is clear: Spam filters are always about collecting as few points as possible.

What do I need to pay attention to?

Trusted Sender

Spam filters usually remember senders who've already been marked as spam on previous occasions. The reputation of your sender is therefore important. More importantly, you have an even better chance if the recipient has entered or saved the sender's e-mail address in his/her address book.

If you send your newsletters or invites with a service like Mailchimp or eyevip, you should have your IT set up an SPF (Sender Policy Framework) record. Thanks to an SPF record, you give the service the right to send e-mails with your sender.

Clean Dispatch List
The golden rule states: always get the explicit consent of your recipient. You can do this in that you always give your recipients the opportunity to unsubscribe from your mailing list. With an "opt out" you reduce possible complaints from angry recipients. Complaints always bring "spam points". In addition, there is a risk that you end up blacklisted.

Always keep your dispatch list up-to-date. If messages couldn't be delivered, you're dealing with a "bounced" e-mail. There are two types:
  • The Soft Bounce
    Der soft bounce is temporary. It is usually caused by a full mailbox or an absence notification from the recipient.
  • The Hard Bounce
    Der hard bounce usually stems from nonexistent e-mail addresses or if the e-mail server is no longer receiving mails.

E-mail addresses that caused a hard bounce should immediately be removed from your dispatch list as hard bounces increase the risk of being classified as spam.

Less is More

Spam filters scan the content of every single e-mail - which is why the content of your newsletter is very important.

Subject Lines and Content
Subject lines and text with CAPITAL letters, multiple exclamation marks or special characters should be avoided. Certain words are also taboo. Not only "Viagra" but also "money", "winner" or "free" are critical words.

The Design 
Deine Newsletter sollte natürlich so wenig wie möglich an einem Spam erinnern. Farbige Schrift in grün, rot, blau oder gelb ist generell zu vermeiden. Auch das Verhältnis Bild/Text sollte ausgewogen sein. Zu viele oder zu grosse Bilder werden als Spam betrachtet. Skripte, die zum Beispiel ein Element auf Klick ein- oder ausblenden würden, haben in einer Newsletter nichts zu suchen und gelten auch als Spamverdächtigt. 

Of course, your newsletter resemble spam as little as possible. Letters in green, red, blue or yellow should generally be avoided. Make sure that the image to text ratio is also balanced. It's also wise to avoid too many or late images, as these are often considered as spam. Texts that show or hide an item on click, for example, also shouldn't be found in a newsletter and are also considered spam.

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