Top Email Marketing Agencies: What to Look for and How to Choose

When done right, email marketing delivers one of the highest ROIs in digital marketing—reportedly as much as $36 for every $1 spent. But many companies struggle to get there on their own, which is why working with a professional email marketing agency can be a game-changer.

The challenge? Choosing the right agency from a sea of options. Some specialize in B2B outreach. Others focus on eCommerce or enterprise automation. Some can help with cold email campaigns using purchased data (like what we offer at Gemstone Data), while others stick strictly to opt-in newsletters.

In this guide, we’ll break down:

• What an email marketing agency actually does

• Key traits to look for

• Questions to ask before hiring

• Red flags to avoid

• Whether outsourcing is right for your business

• And how to find the right partner based on your goals

📬 What Is an Email Marketing Agency?

An email marketing agency is a company that manages all or part of your email marketing efforts. This can include:

• Building or managing your contact lists

• Writing and designing emails

• Setting up automated sequences (like onboarding or nurturing campaigns)

• Running A/B tests on subject lines or send times

• Tracking performance metrics like opens, clicks, and conversions

• Ensuring compliance with spam laws and deliverability best practices

Some agencies focus on warm, opt-in audiences using platforms like Mailchimp, Klaviyo, or HubSpot. Others are experts in cold email outreach, working with tools like Instantly, Smartlead, or Lemlist—often used in B2B or lead generation campaigns.

🎯 When Should You Hire an Email Marketing Agency?

Here are signs it’s time to outsource:

• You don’t have an in-house expert managing campaigns

• Your list isn’t growing or converting

• You’re not sure how to segment or target properly

• You want to start emailing a purchased list (and your current tools won’t let you)

• You need help with email deployment, list acquisition, or multi-touch campaigns that include phone and mobile ads

For companies that use data-driven marketing (like Gemstone clients who purchase highly targeted email lists), a good agency can help with campaign deployment, engagement tracking, and compliance management.

✅ What to Look For in an Email Marketing Agency

Not all agencies are created equal. Here’s what you should look for when evaluating options:

1. Experience in Your Industry

Look for an agency that understands your audience, whether you sell insurance, offer home improvement services, or target B2B buyers.

2. List-Friendly Platform Knowledge

Most popular platforms (like Mailchimp) won’t let you email a purchased list. If you’re using third-party data, make sure the agency:

• Works with ESPs that allow purchased or cold lists

• Can help you warm up domains

• Offers compliant deployment services if needed

At Gemstone Data, many of our clients use email marketing agencies in tandem with our lists, or ask us to manage deployment directly.

3. Results-Driven Approach

Ask about KPIs they track:

• Open rates

• Click rates

• Unsubscribes

• Deliverability

• Actual lead conversions

The right agency should be focused on business outcomes—not just design and copywriting.

4. Data Compliance Knowledge

Make sure the agency:

• Follows CAN-SPAM, GDPR, or CASL (depending on your region)

• Uses unsubscribe links, physical address inclusion, and permission-based tactics

• Understands how to legally email purchased contacts (if applicable)

❌ Red Flags to Avoid

Some email marketing agencies look good on paper but may cause issues down the line. Watch for these warning signs:

• They say purchased lists are illegal. (They’re not, if used properly.)

• They use one-size-fits-all templates for all clients.

• They only focus on open rates without connecting to conversions.

• They push tools that aren’t compatible with your data or goals.

• They don't offer transparent reporting or access to campaign metrics.

🧠 Questions to Ask Before Hiring an Email Marketing Company

To make sure they’re a good fit, ask:

1. What platforms do you work with?

2. Do you support cold email or only opt-in campaigns?

3. Can you integrate with my CRM or dialer?

4. How do you measure success?

5. Do you help with list segmentation and targeting?

6. Can you help me clean or verify my list?

7. Can you send on my behalf using your own domain or IP? (important for cold campaigns)

📊 Should You Outsource or Keep It In-House?

It depends on your resources and goals:

If your internal team is already overloaded or unfamiliar with list compliance, hiring an agency is often the most efficient path to results.

🌟 Recommended Use Cases for Gemstone Clients

If you're a Gemstone Data client using our:

• Purchased email lists

• Consumer or B2B data

• Email deployment service

You may want an email marketing agency to help with:

• Ongoing email campaigns post-deployment

• Drip sequences based on opens/clicks

• Retargeting based on email engagement

• Writing custom campaigns for each lead segment

• Combining email with telemarketing and mobile ads

🚀 Final Thoughts: Find the Right Fit for Your Email Goals

Whether you're sending cold emails to purchased lists or nurturing warm leads through automated sequences, the right email marketing agency can help you:

✔ Improve deliverability
✔ Increase open and click rates
✔ Align your message with the right audience
✔ Free up your team to focus on closing leads

The key is finding an agency that understands your goals, your data, and the platforms that work best for your situation.

📞 Need Help Getting the Right List or Sending to It?

At Gemstone Data, we help businesses:

• Build highly targeted email lists for direct outreach

• Deploy emails to purchased lists (so you don’t violate ESP rules)

• Identify the right platforms or partners for ongoing campaigns

👉 Contact us to get a customized list or to ask about our email deployment services.