Overview

At times, the IP address from which you send emails may be marked as spam sender or blacklisted by email service providers, e.g., Gmail, Yahoo, Yandex, etc. As a result, external users may receive emails from Kerio Connect marked as spam. The following error may appear in the logs:

Our system has detected an unusual rate of unsolicited mail originating from your IP address

This article provides the steps to resolve this issue so that the emails are no longer marked as spam or blacklisted.

Depending on the email traffic you're sending (bulk or marketing emails, etc.), the Kerio Connect Public IP address may become blacklisted or marked as a Spammer host in the Known Spam Relay Blocking systems (like SORBS).

From time to time, the user accounts may become compromised, which generates big traffic of spoofed emails, which leads to a decrease in Domain and IP address reputation.

The sender score is in your own control and responsibility and in most cases, not an issue caused by the Kerio Connect configuration.

To improve your emails' reputation and prevent messages from being marked as spam by other vendors, it's recommended to follow the process below.

Solution

Emails are marked as spam based on the details of their origin and content, therefore Kerio Connect itself cannot prevent them by tweaking any internal configurations.

It would be helpful to review the article Detecting Compromised Servers Used for Spamming for information on how to prevent and mitigate the origin of spam.

The following specific steps might prove useful in fixing the problem:

1. Configure the SPF record
   • Note: There are multiple ways to create an SPF record. It is recommended to include the IP address of your server in the SPF record.
     We suggest using the following format (replace 1.1.1.1 with your real IP address):
     v=spf1 mx ip4:1.1.1.1 -all
2. Configure DKIM and DMARC records
   • If you are not sure how to create such records, please contact your Domain Registrar.
   • In the case of Gmail, if your emails are still being blocked by them after configuring the above, then you can answer the questions on their Help Center article Troubleshooting for senders with email delivery issues and then fill out their contact form.
3. Perform an Email Blacklist Check.
   • The blacklist check will test your mail server IP address against over 100 DNS based email blacklists.
   • If you don't know your mail server's address, start with a MX Lookup.
4. It is possible that the block might be on an ISP-level, which can be checked by retrieving a report for your IP from UCEProtect. If this is the case, here is an example of how the report might look like
   • 
   • You need to check with your ISP regarding this and work with them to get the block removed.
5. If your IP has been blacklisted by Microsoft, you can submit the MSFT BlackList Removal Form.

Testing

Emails should not be rejected by other providers anymore, while domain reputation should increase.

Note: Some external email providers have delisting periods, after which the email Domain and IP address becomes clean and is removed from the Blacklist. For more information, please contact the Blacklisting Authority (SORBS, Spamhaus, etc).

Information

5 ways to avoid landing on an ISP blacklist