How to improve the deliverability of your email campaigns: avoiding spam filters

The deliverability (deliverability is defined as the ability of an email to reach the inbox of its recipients. This implies that the email does not end up in the SPAM folder or bounce back (bounces). To avoid being classified as SPAM we must take care of the reputation of the subdomain and the IP from which the message is sent, as well as taking into account some rules in the configuration of the message and the sending.


Anti-spam filters measure different aspects of the email sent to allow or disallow it to enter the inbox. Some factors that determine the deliverability of our messages are:
–          HTML. The HTML must be valid, without syntax errors and well structured. Avoid blank lines in the code.
–          HTML/TEXT. If our email has an HTML layout, we must attach the text version to the email.
–          Blacklist/Whitelist: If our address is accepted in the user's contacts, it will positively affect reputation, whereas if we are marked as SPAM, we will be penalised.
–          Shipping history. Filters have a memory and know the behaviour of a sender (sending frequency, openings, penalties...). Reputation therefore does not depend on a single sending but on the sender's habitual behaviour.
–          Text-image ratio. An image-heavy email with little text is more likely to be classified as SPAM.
–          SubjectYou should avoid words such as "Discount", "Promotion", "Offer", "Free" as well as capital letters and special symbols (e.g. exclamations) in the subject line. There are topics and phrases related to SPAM that are often penalised, such as talking about large amounts of money, weight loss, etc.
–          Volume and speed. Mass mailings and mailings with too high a rate of mailings per minute can be considered SPAM. As far as possible, we should space out mailings to very large mailing lists over time.
–          FromWe must indicate sender and reply address.
–          IP Reputation. The reputation of the sending IP or subdomain is one of the key factors in deliverability. Several factors influence the improvement or penalisation of this reputation. We will discuss these specific factors in the next article.
Remember to always offer the user the possibility to add your address to their contact list and thus ensure the delivery of future emails.