How to Stop Your "Registration Complete" Emails from Landing in Spam
Overview
A configuration that’s easy to forget when building a site:
“Our registration-complete emails keep ending up in spam.”
You need to set up an SPF record and configure reverse DNS lookup.
First, What Is Forward DNS Lookup?
domain — query —> IP address
Suppose you have an email address like the following.
info@hogehoge.jp
Querying the IP address from hogehoge.jp is called a forward lookup.
What Is Reverse DNS Lookup?
IP address — query —> domain
Querying hogehoge.jp from an IP address is called a reverse lookup.
SPF Record
SPF = Sender Policy Framework
It’s a framework that defines the policy of the side sending email.
Why Does Such a Framework Exist?
Because spoofing the sender is trivially easy!
1 | $ echo "TEST" | sendmail -f aiueo@xxxx.jp -t kenzo.xxxxxx.0107@gmail.com |
What Setting Up an SPF Record Means
Setting up an SPF record means that, by specifying the sender’s IP address and domain,
the recipient can verify whether the sender’s email address matches
the IP and domain information configured in the SPF record.
What Configuring Reverse Lookup Means
It lets you compare the domain derived from the sender’s IP address
with the domain tied to the reverse-lookup-configured IP, and
if they differ, judge it to be spoofed.
Services like Gmail have this filter enabled, so
if reverse lookup isn’t configured, your mail ends up in the spam box.
Verifying the SPF Record Setting
1 | $ dig -t TXT <mail domain> |
- Example) gmail.com
1 | $ dig -t TXT gmail.com |
- Example) yahoo.co.jp
1 | $ dig -t TXT yahoo.co.jp |
Verifying the SPF Record Setting in Gmail
- When SPF: NEUTRAL, the SPF record is not configured correctly.
- When SPF: PASS, the SPF record is configured correctly.
That’s all.
How to Stop Your "Registration Complete" Emails from Landing in Spam