How to Hire an Email Marketing Agency (and Why Most Underperform)
Email is the channel most agencies claim to manage well and most underdeliver on. Here's how to hire the exception.
Email marketing agencies manage one of the highest-ROI channels in digital marketing - and yet underperformance is rampant. Why? Because the gap between "running email" and "running email as a strategic growth channel" is enormous, and most buyers can't see the difference until they're six months into a disappointing retainer.
TTGC manages email programmes as part of integrated growth engagements. We've audited dozens of accounts inherited from other agencies and consistently find the same patterns of underdelivery. This guide is designed to help you avoid those agencies in the first place.
Before evaluating agencies, understand what email marketing services should include and what email marketing pricing looks like so you can assess proposals accurately.
Why Email Marketing Agencies Underperform
They focus on send volume, not list quality - a 50,000-email list with 5% engagement is worse than 10,000 with 35%
Automation flows are set up once and never revisited - flows degrade as products, offers, and audiences change
Subject line testing is treated as the only lever - while copy, offer, and sequence logic are ignored
Deliverability is reactive, not proactive - problems are addressed after inbox rates collapse
Reporting shows open rates and clicks, not revenue - the actual business impact is obscured
What a High-Performing Email Agency Does Differently
Strong email agencies start every engagement with a list audit - segmentation health, engagement rates by cohort, domain reputation, and automation flow mapping. They build a testing roadmap for the first 90 days that covers copy angles, offer structures, cadence, and flow triggers. They report on revenue, not just engagement metrics.
Interview Questions That Separate Strong Agencies from Average Ones
Walk me through a flow you rebuilt and what changed in revenue per recipient.
How do you approach list segmentation, and what triggers a segment rebuild?
How do you monitor and maintain sender reputation?
What's your process for refreshing a welcome sequence that was built 18 months ago?
"A great email agency treats your list like a business asset - because it is. If they're only focused on this month's campaign, they're not thinking about what the list is worth in three years." - Mherie Vic Prevendido, TTGC
Choose TTGC if / Choose an Email-Only Specialist if
Choose TTGC if you need email to work alongside your content strategy, social media, and paid acquisition - integrated list growth, retention, and brand voice across every channel. Choose an email-only specialist if your programme is at high maturity (100,000+ engaged subscribers, complex Klaviyo or HubSpot architecture) and you need a team entirely focused on email operations.
Sources
- Litmus - "The 2025 State of Email Report." Litmus, 2025.
- Klaviyo - "Email Marketing Agency Benchmark Report." Klaviyo, 2026.
- HubSpot - "Email Marketing Statistics." HubSpot, 2025.
Find out what your email programme is actually worth - TTGC offers a free email audit.
Book a free Brand and Growth Assessment and see exactly how Through The Glass Creatives would approach it.
