Outgoing Anti-Spam Protection
This article contains the best practices for outgoing email from your server to the internet. These practices must be followed so that your emails do not get filtered, blocked, or marked as spam by the datacenter or other anti-spam organisations.
Why does a datecenter apply protective measures to outgoing emails?
For every IP available with our products and services, the datacenter as an internet service provider, registers and reserves the IP with organisations such as RIPE or ARIN. This means that they appear as the IP abuse contact for litigation in the WHOIS database.
If an IP is reported to organisations such as Spamhaus and SpamCop, which work to combat spam, malicious websites and phishing, then the reputation of the entire datacenter network is at stake.
It is therefore important that the datacenter takes care of the reputation, quality and security of the network, which also forms an important part of your service.
How does the protection system work?
Some datacenters use a system based on the Vade Retro anti-spam technology.
What to do after receiving an email alert
Important steps to take on receiving a block alert BEFORE the affected IP can be unblocked.
- stop sending email (e.g. stop all mail software such as qmail, Postfix, Sendmail etc.)
- check the email queue (e.g. qmHandle for qmail, postqueue -p for Postfix)
- analyse your logs using the Message-ID found in the block alert
- Check if your mail server is not functioning as an open relay. This is sometimes a default configuration. (https://en.wikipedia.org/wiki/Open_mail_relay)
Can I get whitelisted?
It is not possible to get a whitelisting, i.e. a filtering exclusion on the outgoing emails from your server.
We can only assist you with the logs diagnosis, if the Message-IDs are unknown and not part of your legitimate emails or mailing lists.
If you have checked and found that Message-ID are from your legitimate email, you should then ensure that your email messages comply with the RFC and the Best Practices indicated below. If they do comply, you can inform us by sending a sample of your email (including header). Our technical support team will then assist you with the next steps. Simply call our support line or contact us via the email support interface in your manager.
RFC and Best Practices
RFCs (Request For Comments) are documents intended to describe technical aspects of the internet. They are produced and published by the IETF (Internet Engineering Task Force), a group which basically produces and defines standards.
For more information, see: RFC, IETF and Internet Draft
Best practices are recommended methods which are often based on these documents and are intended to advise you on the best way to proceed. In this instance, this means the basic rules to follow so that your emails are not marked as spam.
If your outgoing email volume is very high, you are advised to:
- reserve an IP block dedicated solely to email usage
- provide an 'abuse' address on this block in order to receive complaints
- configure reverses on all IPs correctly
This operation will enable you to simultaneously isolate the IP and domain reputation if you send emails for various domains, to receive the complaints, and thus do what is necessary to get unblocked by various organisations. It also enables you to locate a problem more quickly on a form that uses domain X or Y, as the emails are not sent out from the same IP and don't have the same reverse.
Avoid using spammer keywords in your emails such as “buy” and “last chance”, and avoid capital letters, impersonal subjects, exclamation marks, and % discounts.
Don't forgot to provide an unsubscribe link for people who have not requested to receive your email or who believe it to be illegitimate.
Be particularly careful to ensure that your emails contain the sender's address (or an alias), a subject, and a correct ratio of text, images and links in the body of the message.
FBL - Feedback Loop
This system will enable you to follow up on feedback provided by some internet service providers directly, informing you that their users have marked your message as illicit, and that it has thus been classified as spam. This will enable you to interact with these ISPs directly concerning your reputation. Some FBLs:
Some authentication services enable you to protect your reputation.
- Sender-ID An email authentication technology developed by Microsoft which validates the authenticity of your domain name by verifying the IP address of the sender. This technology is based on the IETF standard:
- SPF Sender Policy Framework is a standard for verififying the domain of the sender. It is based on
- and consists of adding an SPF or TXT field to the domain DNS, which contains the list of IPs authorised to send emails from this domain.
- Reverse DNS Reverse enables your IP to be "translated” into your domain. That allows the domain associated with the IP address to be found.
- DKIM DKIM This standard is described in
- AOL, Google (Gmail) work on this basis. Official website: