Spam still remains a major nuisance in email traffic. However, the protective measures taken by email providers and recipients against spam occasionally tend to filter out legitimate emails from serious providers. We have compiled 12 tips for you on how to avoid the spam classification of legitimate emails.

1. Check your blacklist

Blacklists contain IP addresses/domains of mail servers which have been declared senders of spam. Many email providers run a synchronisation process of the used IP addresses/domains with blacklists. If the IP address/domain can be found on a blacklist, the email will immediately be sorted out or rejected. Since not all providers use all available blacklists, it is recommended to check which specific blacklists are employed by the relevant providers. Within the framework of regular monitoring, you should check whether your own IP or domain data appears on these blacklists. Is this case, an exclusion from the blacklist may be possible. However, this might come at a charge and must be justified by a good reason. New addresses should be checked immediately.

2. Design subject lines simply

The subject line of an email is one of the most sensitive areas for spam checks. It is recommended that you keep the design of the subject line as plain as possible. This means: The overuse of special characters should be avoided in the same way as unnecessary spaces and the use of upper case characters for entire words or even the complete subject line. Even when the subject line gets past the spam filter, it will probably be perceived as dubious by the recipient. The choice of words is also of great importance. Keywords such as “sex” or “viagra” should be avoided – not only in the subject line but throughout the whole email.

3. Use colours sparingly

Text in loud and striking colours such as red or blue should be avoided. Black or – in the case of dark background – white are the best colours to avoid spam classification. You should use as few different colours as possible.

4. Use links instead of attachments

Email attachments are the most common way to distribute viruses and for that reason, emails with attachments are often filtered. If you wish to send a file anyway, it is recommended to link it as an external download.

5. Send multi-part emails

Even HTML elements are sometimes classed as spam. Emails should therefore be sent as multi-part emails – in HTML or text form – or you should allow the recipient a choice through opt-in.

6. Use static IP addresses

Emails should always be sent from static IP addresses. Dynamic IP addresses can often be found on blacklists.

7. Implement opt-ins immediately

If a recipients unsubscribes prior to receiving a newsletter, he should immediately be deleted from the subscription list. Recipients who continue to receive unwanted newsletters despite of their unsubscription are likely to report them as spam at some point. If you wish to access more than one address database, you should synchronise these regularly in order to take into account all unsubscriptions.

8. Practice whitelisting

A general possibility to reduce the type and scope of filter measures, is to improve your own reputation (positive reputation) through whitelisting. Whitelists are positive lists, which accredit a listed sender with a special reputation and secure his emails privileged status by the email provider. You will find more information on whitelisting in this article:

9. Avoid bcc distribution to several recipients

If an email is to be sent to a number of recipients, you should not specify these recipients in the Bcc field. A large number of recipients in the Bcc field is a sign for spam.

10. Watch the file size

The file size of most spam emails is under 20KB. Email newsletters should therefore have a size between 20KB and 50KB.

11. Do not use bad HTML code

HTML code for newsletters should not be generated through common tools such as Microsoft Word. This code may be “unorthodox” and therefore susceptible to spam classification.