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Email Academy: How and why you should set up a custom domain

Setting up a custom sending domain is not just a matter of appearance; it has profound implications for email deliverability, brand trust, security, and control.

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Whether you are sending newsletters, promotional offers, or transactional emails, the domain from which these emails are sent plays a crucial role in determining their effectiveness. Many businesses, especially small and medium-sized businesses (SMBs), often start with free domains provided by email service providers (ESPs) such as Gmail or Yahoo.

Now, while this might seem like a cost-effective, low effort solution and is generally a good place to start, relying on free domains can significantly undermine your email marketing efforts and overall brand image in the long run. When you set up a custom sending domain and do not authenticate it, you are missing out on essential benefits that will enhance your deliverability and protect your brand.

Sinch Mailjet’s Senior Product Manager, Natalie Lynch, and Senior Email Marketing Manager, Julia Ritter, explored why investing in a custom sending domain and authenticating it with your ESP is a smart move for any business in our latest Email Academy series webinar Ensure email delivery success by optimizing your mail domain.

What is a custom sending domain?

First off, we should probably start off by defining what exactly is a custom sending domain.

A custom sending domain is essentially your own personalized address used for sending emails. Typically, as a professional or SMB owner you’ll want a custom sending domain that matches your business website and aligns with your brand. So, for example, if you ran a hand-made shirt business in Barcelona with a website domain name of, your email marketing should be sent from the same domain.

Instead of sending from a free domain address such as you can send from an address that reflects your company or brand.

Here are a few examples:


Cust­om doma­in name­


Firs­t name­

Cust­om doma­in name­

Last­ name­











What is a free domain?

A free email sending domain, on the other hand, is typically a domain provided by an inbox service provider that you can use to send emails without having to set up your own custom domain. These domains are often shared among many users and are usually branded with the ESP's domain name.

While convenient, using a free email sending domain comes with several limitations compared to using a custom domain, which we’ll go through now.

Why use a custom domain when a free domain is so easy?

Setting up a custom sending domain offers several advantages that can significantly enhance your email marketing efforts. Here are the key benefits:

Spoofers and phishers love free domains

Free email services typically have less stringent oversight and monitoring compared to custom domains. This means that malicious activities can often go unnoticed for longer periods, allowing phishers to operate with less risk of immediate detection. While most free email providers have policies against abuse, the sheer volume of users makes it difficult to enforce these policies effectively. This provides a relatively safe haven for malicious actors to exploit.

OK, that’s all well and good you might ask, but what does it have to with me?

Email spoofing is a form of phishing where scammers send fraudulent emails designed to look like they came from a trustworthy, recognizable brand. The goal is to collect account credentials, financial information, or other data that lets cybercriminals carry out their dirty deeds.

Infographic displaying the steps used in email brand spoofing

If persistent attempts are made by spoofers to send fraudulent mail on your behalf, it will erode customer confidence in your brand. Something you want to avoid. By setting up a custom domain, you make it much harder for cybercriminals to imitate your brand and protect your subscribers from phishing attacks.

Build brand credibility in the inbox

Getting subscribers to open your emails can be hard enough at the best of times. And with the rise of spoofing, phishing scams, and other cyberattacks, consumers are more skeptical of emails than ever before. You really don’t need another reason for subscribers to ignore your emails or worse, send them to the spam folder.

So, a couple things you can do to increase brand trust in the inbox is register a custom domain and authenticate it with your ESP. Emails sent from a custom domain appear more professional and trustworthy to subscribers, potentially leading to an increase in open rates as recipients recognize that brand domain.

Email authentication

When setting up a custom domain, you are encouraged to properly configure your email authentication protocols to verify your identity as an email sender and ensure the integrity of your messaging. This is extremely important as it not only boosts your email deliverability and chances of landing in the inbox, but also adds a tighter level security to your campaigns.

The three primary protocols are:

  1. SPF (Sender Policy Framework): This protocol allows domain owners to specify which IP addresses are authorized to send emails on behalf of their domain. It helps recipients' mail servers verify that the email is coming from an authorized source, increasing deliverability.

  2. DKIM (DomainKeys Identified Mail): DKIM adds a digital signature to the email header, which is created using a private key. The recipient's mail server uses the public key, published in the sender's DNS records, to verify that the email was indeed sent from the stated domain and has not been altered in transit, protecting your brand.

  3. DMARC (Domain-based Message Authentication, Reporting, and Conformance): DMARC builds on SPF and DKIM by adding a policy framework that specifies how to handle emails that fail authentication checks. It also provides a mechanism for receiving reports on email authentication results, helping domain owners monitor and improve their email security.

IMPORTANT: Google and Yahoo announced that as of February 2024, DKIM and SPF authentication will be mandatory for bulk email senders. These senders will also need to have DMARC set up at p=none policy. For more information about how to implement DKIM and DMARC and comply with the upcoming mandates, check out our articles How to handle SPF, What is DMARC and how it works and How to set up DKIM in 3 easy steps.

Improve sender reputation

A custom domain helps build a positive sender reputation. But what is your sender reputation? Well, different inboxes and internet service providers (ISPs) use different proprietary scoring algorithms to calculate your sender score, but all are more or less based on similar parameters:

  • Your sending history

  • Number of spam complaints associated with your domain name

  • Number of spam traps your emails snag

  • The different authentication protocols you set (SPF, DKIM, DMARC…)

If recipients flag your messages as spam, your email reputation suffers, and future messages may be more likely to wind up in the junk folder. It's a vicious cycle – getting flagged as spam leads to a bad reputation, and a bad reputation increases the chances you'll be flagged again.

ISPs track the sending behavior of domains, and a consistent sending domain can help maintain a good reputation, leading to better inbox placement.

GDPR and CAN-SPAM compliance

Setting up a custom email domain can also significantly aid in your compliance with data regulation acts such as General Data Protection Regulation (GDPR) and the CAN-SPAM Act. Enhanced security measures can only be implemented through customs domains, such as the email authentication protocols we mentioned earlier. This helps prevent email spoofing and phishing attacks, protecting user data and ensuring secure communication.

Also, emails sent from a custom domain clearly identify the sender, helping ensure that users know who is contacting them. This is crucial for obtaining informed consent for data processing and for providing clear opt in options as required by GDPR.

Pro tip: Looking for guidance on following data privacy laws, including GDPR, CCPA and HIPAA plus advice on how to use email authentication to protect your contacts, your reputation, and your email deliverability? Our sister company Sinch Mailgun recently published an email and security compliance guide that runs through all you need to know.

You can watch the full webinar, where our experts Julia Ritter and Natalie Lynch discuss how to secure email delivery success by optimizing your mail domain.

Setting up a custom domain

Setting up a custom sending domain involves several steps, including domain validation and authentication. Here is a quick, step-by-step walkthrough:

Step #1 – Choose and register your domain

Before you can set up a custom sending domain, you need to have a domain registered (if you haven’t done so already). This can be done via several popular sites such as GoDaddy, IONOS, or Google Domains.

Step #2 – Choose an ESP

Once you have registered your domain name, the next step is to choose an ESP. Clearly, there’s only one real choice here for a secure, fast, trustworthy option and that’s Sinch Mailjet. Of course, while we confidently back our own product there are many ESPs for you to choose from.

Step #3 – Configure your DNS settings

Now you’ve chosen your domain and ESP provider, you’ll need to access your domain’s DNS settings through your domain registrar to add several DNS records and configure your custom domain.

The reason for adding these TXT type records is so that your ESP can verify that you actually own the domain name. ESPs require this step to protect your sending domain from the very start.

Step #4 - Authenticate your domain

After validating your domain, we strongly recommend that at a minimum you set up the first two of the three additional email authentication records:

  • SPF (Sender Policy Framework)

  • DKIM (DomainKeys Identified Mail)

  • DMARC (Domain-based Message Authentication, Reporting, and Conformance).

They work in conjunction to validate a sender's identity, prevent email spoofing and phishing attacks, and email deliverability.

Wrapping up

So, while setting up a custom sending domain may seem to involve several technical steps, it’s actually incredibly simple and quick to do! By taking the time to follow the processes outlined in the article, you ensure that your emails are authenticated correctly and are less likely to be marked as spam or rejected by recipient servers.

Expert advice on custom domain set up

The team at Sinch Mailjet will be more than happy to answer any questions, doubts, or queries you might have when it comes to setting up your custom domain.

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