[Definitive Guide] Emails not arriving!? 3 common DNS configuration mistakes and how to fix them

[Definitive Guide] Emails not arriving!? 3 common DNS configuration mistakes and how to fix them

Hello, Toshi (@josys_rescue) here.
When you are in charge of Web or IT at a small or medium-sized business, there is one trouble you will definitely face at least once.
That is—

Moreover, the cause is often not the server or the settings, but
actually DNS (Domain Name System) in many cases.

This time, I have compiled 3 typical DNS configuration mistakes that cause such "email delivery failure troubles," along with solutions that have actually proven effective in the field.

🧭 What is DNS? (Understand it in roughly 1 minute)

DNS stands for "Domain Name System," and it acts like an "address book" on the internet.
For example,

For example,

• Indicates the location of the mail server → MX record

• Location for displaying a website → A record

In other words, if the DNS settings are wrong, emails will not arrive correctly is the reason.

🚨 Common DNS configuration mistake #1: Missing MX record settings

The most common one is the "MX record is not registered" pattern.

🔍 Symptoms

• Emails from outside do not arrive

• Even when sent from Gmail or Outlook, they return as "Recipient unknown"

• You can send but cannot receive

🧰 Solution

1. Check the MX information for the mail server you are using (e.g., Xserver, Google Workspace, etc.)

2. Configure the DNS management screen as follows
   Hostname: @
   Type: MX
   Value: 10 sv〇〇〇.xserver.jp.
   

3. After saving, it will take anywhere from a few hours up to 24 hours to propagate.
   

⚙️ Common DNS Configuration Mistake #2: Old MX Records Remaining

This happens when previous MX records remain after migrating servers.

🔍 Symptoms

• Some emails arrive, but emails from other domains do not

• Emails arrive intermittently

🧰 Solution

1. Delete old MX records and keep only the correct ones

2. Organize the priority (lower numbers have higher priority)

3. When in doubt, the standard practice is to narrow it down to just one.
   

🧱 Common DNS Configuration Mistake #3: TTL is too long, preventing changes from reflecting

TTL (Time To Live) is the "time to keep the configuration cache." If this is too long, it becomes a pitfall where
changes are not reflected immediately even after fixing them.

🔍 Symptoms

• Changes do not reflect immediately after fixing the settings

• Emails arrive correctly in some environments but not in others

🧰 Solution

• Before making important changes, set the TTL to a short value (e.g., 300 seconds = 5 minutes)

• Once the fix is complete, return it to the normal value (e.g., 3600 to 86400)

• Manually clearing the DNS cache is also effective when you want to reflect changes immediately

💡 Advice from Toshi

DNS configuration is a world where a single typo can stop all communication.
However, once you understand how it works, it is nothing to be afraid of.

Especially for the "solo IT administrator" in small and medium-sized enterprises,
DNS is the #1 piece of knowledge that prevents trouble when you understand it is.

🧰 Related Articles

• [2025 Edition] A Thorough Comparison of Xserver and ConoHa! How to Choose for Beginners and SMEs

• [Definitive Guide] A Checklist to Ensure You Never Forget to Renew Your SSL Certificate

📩 Finally

If you found this article helpful,
I would be encouraged if you could support me by following or clicking the like (♡) button.

Please feel free to let me know in the comments if you "got stuck here" or "want me to explain this setting too."

I hope your daily life becomes even a little bit easier.

— Toshi (Solo IT Admin Rescue)