DKIM (DomainKeys Identified Mail) adds a digital signature header to an email, helping verify that it wasn’t altered in transit and actually came from the specified domain.

DMARC builds on SPF and DKIM. It lets you specify how emails that fail these checks should be handled (e.g., quarantined or rejected) and provides reports about how your domain is being used.

Where can I find my domain’s SPF, DKIM, and DMARC values?

Your installed mail app (e.g., Mailu) displays these values in its own interface. Add them as TXT records in the DNS section of your domain management area.

Web Hosting: Optimizing Email Deliverability

Your web hosting now runs as its own VPS with a self-installed mail server (e.g., Mailu). Learn how to optimize SPF, DKIM, DMARC, reverse DNS, and IP reputation for reliable delivery → Learn more

10 November 20265 min read0 Views0 helpful

Introduction

Are you running your own mail server on your web hosting (VPS Cloud) through One-Click Apps—for example, Mailu—and noticing that some emails aren’t being delivered successfully? You’re in the right place. Several factors need to be considered to ensure reliable email delivery. In this guide, you’ll learn about the most important factors that affect email deliverability and how to improve the reliability of your emails.

Info

Haven’t set up your own mail server yet? This article assumes that you’ve already installed your own mail server through One-Click Apps (e.g., Mailu). The initial setup—installing the app, adding DNS records, and creating mailboxes—is covered in the article “Web Hosting: Setting Up Email.” This article covers only the subsequent optimization of deliverability.

Web Hosting: Optimizing Email Deliverability

Your Own IP Instead of Shared Infrastructure

Since your web hosting product is now a VPS, your mail server runs on your VPS’s own IP address—not on infrastructure shared with many other customers. The key advantage is that the reputation of this IP address depends entirely on your own email traffic, not on the behavior of other customers. This makes it all the more important to implement the following steps correctly so your IP address can build and maintain a good reputation.

Meeting Authentication Standards (SPF, DKIM, DMARC)

Authentication standards make things easier for email providers and mail servers by helping verify the sender’s legitimacy. Three important authentication standards have been established to prove that you’re authorized to send emails on behalf of a domain: SPF, DKIM, and DMARC.

SPF (Sender Policy Framework): SPF helps prevent email spoofing by specifying which IP addresses are authorized to send emails on behalf of a domain. For example, you can add an SPF record in the DNS settings for your “example.com” domain to define which mail servers are allowed to send emails from “@example.com.” If an email is sent from an unauthorized server, the receiving mail server may mark it as suspicious or reject it.

DKIM (DomainKeys Identified Mail): DKIM adds a digital signature header to an email. This helps verify that the email wasn’t altered in transit and actually came from the specified domain. The receiving mail server uses this signature to check the email’s integrity.

DMARC (Domain-based Message Authentication, Reporting & Conformance): DMARC builds on SPF and DKIM and adds another layer of protection. It lets you specify how emails that fail SPF or DKIM checks should be handled (e.g., quarantined or rejected). DMARC also provides reports showing how your domain is being used in emails, helping you monitor potential abuse.

Warning

Values come from your mail app Your installed mail app (e.g., Mailu) displays the exact SPF, DKIM, and DMARC values for your domain in its own interface. Then add these values as TXT records in the DNS section of your domain management area. For details on the initial setup, see the article “Web Hosting: Setting Up Email.”

Set Reverse DNS (PTR Record)

In addition to SPF, DKIM, and DMARC, many receiving mail servers also check whether your mail server’s IP address has a matching reverse DNS record (PTR record)—that is, whether a reverse lookup of the IP address points to a hostname that matches your sending domain (e.g., mail.yourdomain.com). If this record is missing or points to a generic hostname, many providers consider that a sign of spam.

You can set the PTR record for your VPS’s IP address directly in the ZapX customer panel:

Open your VPS in the customer panel.
Go to the Settings → Reverse DNS tab.
For your VPS’s primary IP address, enter the hostname your mail server uses as its own name (the same value you would normally set as the MX or A record).

Tip

Your PTR record and hostname should match Ideally, the PTR record (IP → hostname) should match your mail server’s A record (hostname → IP). This is known as “Forward-Confirmed reverse DNS” (FCrDNS). It’s one of the simplest ways to build trust with many major email providers.

IP Reputation and Warmup

Even with your own dedicated IP address, it takes time to build a good reputation. Keep the following in mind:

Increase sending volume gradually (warmup): If you send a large number of emails all at once from a new IP address, many providers will consider it suspicious. Instead, start with a lower sending volume and increase it gradually over several days or weeks.
Monitor bounces and spam complaints: A high number of invalid addresses (bounces) or spam reports from recipients can permanently damage your IP address’s reputation. Clean your recipient lists regularly.
Use your IP responsibly to avoid being blacklisted: If a provider blacklists your IP address because of abuse (e.g., compromised credentials or mass spam), your emails may no longer be delivered or may be marked as spam. Monitor your mail server for suspicious activity and consistently use your mail app’s spam filters to prevent this from happening. If you do end up on a blacklist, use a common blacklist checker (e.g., mxtoolbox.com) to find out which list you’re on. You can usually submit a delisting request directly through that list.

Content Best Practices

Email content also plays an important role. Aim for a balanced ratio of text to images. Also avoid potentially problematic content such as videos, JavaScript, or forms, as these can trigger spam filters or cause delivery issues. Every email should also include an unsubscribe option and a legal notice at the end.

Other best practices include using clear and concise language, avoiding overly aggressive marketing messages, and optimizing emails for mobile devices.

Testing and Reliability

Before using your mail server in production, or if you suspect delivery issues, it’s worth checking your DNS configuration:

Use our free Email DNS Health Checker to check your domain’s SPF, DMARC, MX, and—where possible—DKIM records online and get clear explanations of any issues found.
External services such as mail-tester.com and mailgenius.com go a step further: You send a test email to the address they provide, and the service evaluates factors such as content, headers, SPF/DKIM/DMARC, and blacklist status, then gives you specific recommendations for improvement.

These tools are especially useful for making sure your emails are configured correctly, improving deliverability, and avoiding common issues that could cause your emails to be marked as spam.

Conclusion

If you’ve followed and implemented all the recommendations, you should now be in a much better position to ensure the security and reliability of your email delivery. Your emails are more likely to be delivered and are also better protected against unauthorized access and abuse.

If you need help setting up or optimizing your mail server, our support team is always happy to assist.

FAQ

Frequently asked questions

It’s for anyone who has already set up their own mail server through One-Click Apps (e.g., Mailu) on their web hosting (VPS Cloud) and is having trouble delivering some emails. The initial setup is covered in the article “Web Hosting: Setting Up Email.”

Your mail server runs on your VPS’s own IP address, not on infrastructure shared with other customers. This means the IP address’s reputation depends entirely on your own email traffic.

SPF (Sender Policy Framework) helps prevent email spoofing by specifying which IP addresses are authorized to send emails on behalf of a domain.

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Web Hosting: Optimizing Email Deliverability

Introduction

Your Own IP Instead of Shared Infrastructure

Meeting Authentication Standards (SPF, DKIM, DMARC)

Set Reverse DNS (PTR Record)

IP Reputation and Warmup

Content Best Practices

Testing and Reliability

Conclusion

Frequently asked questions

Web hosting

Your Own IP Instead of Shared Infrastructure

Meeting Authentication Standards (SPF, DKIM, DMARC)

Set Reverse DNS (PTR Record)

IP Reputation and Warmup

Content Best Practices

Testing and Reliability

Conclusion

Game Server

Servers & Hosting

ZAPX

Resources

ZAP-Hosting