How to set up custom sending domains in Mailrush for better inbox placement

If you’re sending cold emails or outreach campaigns, you’ve probably noticed: getting into the inbox is a lot harder than it used to be. Using the default sender options in your email platform is almost a guarantee your messages wind up in spam or get ignored. If you want better inbox placement—and, honestly, if you want to look like you know what you’re doing—you need to set up a custom sending domain. This guide is for anyone using Mailrush who wants to get their emails actually seen.

Let’s break this down step by step, with the goal of getting you set up quickly and avoiding common headaches.

Why bother with a custom sending domain?

Before we get into the weeds, here’s the deal: using your own domain (like mail.yourcompany.com) instead of a generic Mailrush sender does a few important things: - You look legitimate. Your emails come from your brand, not some sketchy relay service. - You control your reputation. If someone else using Mailrush gets blacklisted, it won’t drag you down. - You can set up authentication. This is huge for deliverability (think SPF, DKIM, DMARC—more on those soon).

The flip side? It takes a little work, and you need access to your domain’s DNS settings. But it’s not rocket science. If you’re sending any real volume, it’s worth the effort.

Step 1: Prep your domain (and your expectations)

First things first: don’t use your main company domain for cold outreach. If you burn your core domain’s reputation, you’ll have bigger problems than bad inbox rates. Instead: - Register a variation. Something like yourbrandmail.com or getyourbrand.com works. - Warm it up. New domains are suspicious to spam filters. Start slow—send a few real emails, get some replies, let it age for a couple weeks if you can.

Pro tip: Make sure your domain has a proper website or landing page. Empty domains look spammy to filters (and to humans).

Step 2: Add your domain in Mailrush

Once you’ve got your sending domain ready, it’s time to plug it into Mailrush.

  1. Log in to Mailrush.
  2. Go to the Settings or Sending Domains section.
  3. Click Add Domain (or similar—it’s pretty obvious).
  4. Enter the subdomain you want to use for sending, like mail.yourbrandmail.com.

Mailrush will spit out a handful of DNS records you need to add. Don’t panic—this is normal, and you only have to do it once per domain.

Step 3: Update your DNS records

This is where most people get tripped up. Here’s what you’ll usually see:

  • SPF record – Authorizes Mailrush servers to send emails for your domain.
  • DKIM record – Adds a cryptographic signature to prove your emails aren’t forged.
  • Return-Path (CNAME) – Handles bounces and feedback loops; sometimes called “tracking” or “bounce” domain.
  • DMARC record (optional, but recommended) – Tells receiving servers what to do if SPF/DKIM checks fail.

How to add these records

  1. Log in to your DNS provider (wherever your domain is hosted: GoDaddy, Namecheap, Cloudflare, etc.).
  2. Find the DNS or zone editor.
  3. Add each record exactly as shown in Mailrush.
    • Copy-paste everything. Don’t “improve” anything.
    • For CNAMEs, make sure you don’t duplicate the domain (e.g., mail.mail.yourbrandmail.com is wrong).
    • Save after each record.

DNS changes can take anywhere from a few minutes to 24 hours to propagate. Don’t keep clicking “verify” in Mailrush every ten seconds. Go get a coffee.

Step 4: Verify authentication in Mailrush

Once you’ve added the DNS records: 1. Go back to Mailrush and click Verify or Check DNS for your new domain. 2. If you did everything right, you’ll see green checkmarks for SPF, DKIM, and CNAME. 3. If not, double-check for typos or missing dots. Seriously, 90% of problems are tiny copy-paste mistakes.

What if it still won’t verify? - Wait an hour and try again. - Make sure you’re not mixing up root domains and subdomains. - Check if your DNS host uses “automatic” or “@” shorthand—if in doubt, ask their support.

Step 5: Set up DMARC (don’t skip this)

DMARC isn’t required, but it’s worth it. It’s basically a public instruction for mail servers: “if an email fails SPF or DKIM, here’s what to do.” Even a basic DMARC policy improves your credibility.

How to add a DMARC record: - Add a new TXT record for _dmarc.yourbrandmail.com - Use this as the value:

v=DMARC1; p=none; rua=mailto:you@yourbrand.com

  • This policy just monitors (doesn’t reject anything). You can get stricter later if you want.

Step 6: Set up a custom “from” address and test

Now, in Mailrush, pick an email address under your new domain—like alex@mail.yourbrandmail.com. This is what your recipients will see.

  • Send test emails to Gmail, Outlook, and Yahoo.
  • Check all folders (including spam and “promotions”).
  • Look for “sent via Mailrush” or “on behalf of” warnings—if you see those, something’s off with your authentication.

If your test emails look clean and hit the inbox, you’re good to go.

What actually improves inbox placement (and what doesn’t)

Here’s where people get lost in the weeds. Setting up a custom sending domain and getting authentication right does help your deliverability. But it’s not magic. You’re still subject to:

  • Content filters. Spammy subject lines, too many links, or weird attachments will tank your emails.
  • Sending volume spikes. Don’t go from zero to 5,000 emails a day. Ramp up slowly.
  • List quality. Old or scraped lists will get you flagged, no matter how well you set up your domain.
  • Engagement. If nobody opens or replies, your reputation drops fast.

Ignore: Fancy “deliverability hacks,” blackhat tricks, or promises of instant inboxing. If something sounds too good to be true, it is.

Pro tips and common pitfalls

  • Always use a subdomain (like mail. or outreach.) instead of your root domain for sending.
  • Separate transactional and cold email domains. Don’t risk your customer receipts on outreach reputation.
  • Monitor your DNS records. Sometimes, DNS hosts reset or overwrite things without warning.
  • Don’t rely only on Mailrush’s built-in tools. Use third-party deliverability testers like mail-tester.com or GlockApps to see how your setup scores.

Keep it simple—and keep testing

Setting up a custom sending domain in Mailrush isn’t complicated, but it’s easy to overthink. Get your DNS records right, start small, and pay attention to your results. If your emails start landing in spam, don’t panic—check your authentication, slow down your sending, and make sure your content sounds like a real human.

It’s not about chasing perfect scores or every new trick. Just build trust with the mail servers (and the people you’re emailing), and you’ll see better inbox placement over time. Iterate as you go, and don’t be afraid to ask for help if you get stuck.