Cómo configurar un dominio de seguimiento personalizado (CNAME) para firmas de correo electrónico

Email tracking is broken by default. When you embed a pixel or a link in a signature, it loads from your tracking provider's domain — tracking.example.io or open.yourvendor.com. Gmail and Outlook render those fine, but corporate mail filters, Barracuda, Proofpoint, and Mimecast often block them outright because the domain is not your own. A custom tracking domain (CNAME) solves this by routing tracking traffic through a subdomain you control, so the request looks like it came from tracker.yourcompany.com instead of a third-party server. Here is exactly how to set one up, what records to add, and what to expect from each major mail client.

Why you need a custom tracking domain

Every time someone opens an email with a tracked signature, their mail client makes an HTTP request to load a tiny invisible image. If that request goes to a domain that is not your company's, security filters treat it as a potential phishing or tracking beacon. The result: the image never loads, the open is never recorded, and your click-through link may be rewritten or blocked.

A custom tracking domain solves two problems:

Deliverability: The request originates from your own domain, so it passes SPF, DKIM, and DMARC alignment checks that many enterprise filters enforce.
Data accuracy: Without a CNAME, you lose up to 30% of open and click data on corporate recipients. With a CNAME, that number drops to near zero because the request is not flagged.

The setup is straightforward: you create a CNAME record that points a subdomain (e.g., track.yourcompany.com) to your tracking provider's server. Then you configure your provider to use that subdomain for all tracking assets.

Prerequisites and DNS basics

Before you touch your DNS provider, confirm you have:

Access to your domain's DNS management console (Cloudflare, AWS Route 53, GoDaddy, Namecheap, or whatever you use).
Permission to add a CNAME record. Some corporate DNS setups restrict this — you may need to ask your IT team.
A tracking provider that supports custom domains. Most do, but verify in your account settings.

A CNAME record maps a name to another name. It is not an A record (which points to an IP). For email tracking, you will create something like:

track.yourcompany.com  CNAME  track.newmailclick.com

The exact target depends on your provider. newmail.click, for example, provides a unique CNAME target in your account dashboard under "Tracking Domain".

Important: CNAME records cannot coexist with other record types at the same name. If you already have an MX, TXT, or A record for track.yourcompany.com, you must remove it first. Use a subdomain that has no existing records.

Step-by-step CNAME setup

1. Choose your subdomain

Pick something short and predictable. Common choices:

track.yourcompany.com
open.yourcompany.com
link.yourcompany.com
email.yourcompany.com

Avoid click.yourcompany.com — some mail filters flag the word "click" as suspicious. Stick with track or open.

2. Get the CNAME target from your provider

Log into your tracking provider's settings. Look for "Custom Tracking Domain", "CNAME Setup", or "Branded Domain". Copy the target hostname they give you. It will look something like:

track-abc123.newmailclick.com

Do not guess this. Each provider generates a unique target per account.

3. Add the CNAME record in your DNS

Go to your DNS provider and add a new record:

Type: CNAME
Name: track (or whatever subdomain you chose)
Target: the hostname from step 2
TTL: 300 seconds (5 minutes) or the lowest allowed value

If your DNS provider uses a "Host" field, enter just the subdomain label (e.g., track), not the full domain. If it uses "Alias" or "Canonical name", paste the full target.

4. Wait for propagation

DNS changes propagate in minutes to hours. Cloudflare and Route 53 usually update within 60 seconds. GoDaddy can take up to an hour. Use a tool like dig track.yourcompany.com CNAME or nslookup to confirm the record resolves to the target.

5. Verify in your provider

Back in your tracking provider, click "Verify" or "Save". The provider will check that the CNAME resolves correctly. If it fails, double-check the record type and target — a common mistake is using an A record instead of CNAME.

How different mail clients handle the custom domain

Not all email clients treat tracking images the same way. Here is what you can expect after setting up your CNAME.

Gmail (web and mobile)

Gmail caches images on its own proxy servers. Even with a custom domain, Gmail will still proxy the request through lh3.googleusercontent.com. The tracking image loads, but the referrer and some metadata may be stripped. You will still get an open event because the image request reaches your server — it just comes from Google's IP instead of the recipient's. This is fine. The CNAME ensures the request is not blocked before it reaches Google's proxy.

Outlook (desktop and web)

Outlook's default behaviour is to block external images. When a user clicks "Download Pictures", Outlook makes a direct request to the image URL. If that URL is on a third-party domain, Outlook may still block it depending on the Exchange Online Safe Sender policy. With a custom domain, the request comes from your company's domain, so Outlook treats it as trusted. This is the single biggest win of a CNAME — Outlook open rates typically double after setup.

Apple Mail (macOS and iOS)

Apple Mail does not block images by default. It loads them directly from the source. A custom domain here is less about deliverability and more about privacy. Apple's Mail Privacy Protection (MPP) pre-loads images on Apple's servers, so you will see inflated open counts regardless of your domain. The CNAME still helps with click tracking — links that point to your custom domain are less likely to be rewritten by corporate proxies.

Corporate filters (Barracuda, Proofpoint, Mimecast)

These are the primary reason to set up a CNAME. They inspect every link and image request. If the domain does not match the sender's domain, they either block it or rewrite the link to go through their own inspection proxy. A custom domain that matches your sending domain passes the domain alignment check, so the filter lets it through. No rewrite, no block.

How newmail.click handles this

In newmail.click, you can set up a custom tracking domain from the Settings page under "Tracking Domain". The free signature builder works with any domain — you do not need a custom CNAME to use the editor. If you upgrade to Pro, click and open tracking use your custom domain automatically once you configure the CNAME. Pro also sends Slack and email alerts when someone opens or clicks, and it applies default UTM parameters to any links you add to your signature. We do not offer team plans, SSO, or SCIM — this is a straightforward tool for individuals and small teams who need reliable tracking without enterprise overhead.

Common mistakes and how to avoid them

Using an A record instead of a CNAME

An A record points to an IP address. Tracking providers give you a hostname, not an IP, because they need to load-balance across multiple servers. If you use an A record, the tracking will break when the provider changes their infrastructure. Always use CNAME.

Forgetting to remove existing records

If track.yourcompany.com already has an MX or TXT record, you cannot add a CNAME at the same name. Delete the old record first. If you need both, use a different subdomain (e.g., tracker instead of track).

Not waiting for propagation

You verify the CNAME two minutes after adding it, it fails, you panic, you change things, you break it. Wait at least 10 minutes. Use dig with a short TTL to confirm.

Setting the TTL too high

A TTL of 86400 seconds (24 hours) means any change you make takes a full day to propagate. Set it to 300 seconds during setup, then increase it to 3600 or higher once everything works.

Skipping verification in the provider

Adding the DNS record is only half the job. You must also tell your tracking provider to use that domain. If you skip the verification step, your provider will keep serving tracking assets from their default domain.

Testing your setup

After verification, send a test email to yourself and to a colleague who uses a corporate email (e.g., a Gmail Workspace or Outlook account behind a filter). Open the email and check:

Does the tracking image load? (Look for a tiny pixel in the signature area.)
Does the click link redirect correctly?
In your provider's dashboard, does the event show the correct domain?

If the image does not load, inspect the email source. Look for an <img> tag with a src attribute that contains your custom subdomain. If it still shows the provider's default domain, you missed the configuration step inside the provider.

If the image loads but no event is recorded, check that your provider's server is reachable from the recipient's network. Some corporate networks block all outbound HTTP requests to non-approved domains — a custom domain solves this only if the domain is on the company's allowlist. In that case, ask the recipient's IT team to add track.yourcompany.com to their allowlist.

When a CNAME is not enough

A custom tracking domain solves the domain reputation problem, but it does not fix every issue:

Mail Privacy Protection (MPP): Apple's proxy will still pre-load images, inflating open counts. No CNAME can stop this.
Image blocking by default: Outlook and Gmail still require the user to enable image loading. A CNAME only helps once they do.
Link rewriting: Some corporate proxies rewrite all links, even those on trusted domains. A CNAME reduces the chance but does not eliminate it.

If you need to bypass MPP entirely, you must use a different tracking method (e.g., server-side open detection via SMTP logs), which is beyond the scope of signature tracking.

Set up your custom tracking domain today and stop losing data to corporate filters. Try the Pro trial — 7 days, no card.