I have been trying to learn about phishing emails. I have read up quite a bit on it. I setup a domain somthing.tk (free domain), hosted a website on a VPS (Digital Ocean). Set up my own mail transfer agent (Postfix).

Now I have set up:

  1. DKIM
  2. DMARC
  3. SPF

All pass in GMail when I send the mail, but still the mails send by me are flagged as spam by GMail spam filter. What am I doing wrong?

Also I am using GNUMail to send emails via this command:

echo "anything" | mail -s "subject" [email protected]

  • 1
    When Gmail puts a message in Spam, there's a giant banner at the top that says "Why is this message in spam?" followed by the answer. What does that say for your emails? Commented Mar 10, 2019 at 17:57
  • Why is this message in Spam? It's similar to messages that were detected by our spam filters.
    – yeah_well
    Commented Mar 10, 2019 at 18:04
  • then it is not the transport layer that it is detecting but the content
    – schroeder
    Commented Mar 10, 2019 at 18:22
  • should i not use gnu mail?should i use it but increase my content?
    – yeah_well
    Commented Mar 10, 2019 at 18:35
  • 1
    I bet using .tk has something to do with this. The same setup with .icu seemed to work fine. Not anymore! TLD reputation matters. Commented Mar 10, 2019 at 18:52

1 Answer 1


Unfortunately, .tk is one of the TLDs that are notoriously associated with certain threat actors and are used by malware to establish C2 channels (malware home-calling).

SNORT and Suricata (two most widely-used opensource IDS/IPS solutions) even have detection rules written for .tk, .pw and .ru URLs, it would generate an alert for the SOC analysts every time a hit is recorded against them in the network.

I'd suggest using a purchased domain name to get past the email filters. GL!

BONUS: You might want to check your URL/domain names at https://www.urlvoid.com to see if they're marked malicious or suspicious by security vendors/spam databases.


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