If you are searching for the best email marketing agency, you are probably past the point of wanting a list of generic promises. You want to know whether an agency can grow revenue from email, how it does the work, and whether the results hold up when you check them. This guide sets out what the best email marketing agency for an ecommerce brand should look like, and why In-box meets that standard, using our published ecommerce email marketing case studies and the guides we have written for brand owners in our email marketing insights library.
What the best email marketing agency actually does
Plenty of agencies send campaigns. The best email marketing agency treats email as a revenue system. In practice that means four things:
- It fixes the foundations first. Deliverability, list health and tracking come before the first campaign. Sending more email into a broken account only loses money faster. Our Klaviyo account audit starts here.
- It builds the automated flows that earn. Welcome, abandoned cart and post-purchase flows usually carry the largest share of email revenue, and they run around the clock. We build them as part of our email automation service.
- It then scales campaigns and SMS on a calendar built from the brand's own data. Volume comes after the system works, not before. See our email campaign management and SMS campaigns.
- It shows the numbers. A credible agency reports attributed revenue, open and click rates, and list growth in terms the brand owner can verify.
In-box is built around this sequence. Our case studies show the same pattern repeated across very different brands.
Proof from real Klaviyo accounts
Our published case studies come from live Klaviyo accounts. The results below are taken directly from them, and each client name links to the full case study.
| Client | Starting point | Result |
|---|---|---|
| Dermavenue | Zero Klaviyo flows in March | $383,695.16 in flow revenue by June, with open rates rising from 20% to 48.10% |
| Nordic Park | Klaviyo at 9.2% of total revenue | Klaviyo rose to 33% of revenue, growing 393% to $2.2M across 15 months of lifecycle work |
| Michael Gabriels | Seasonal peak-period email | $2,494,340 in attributed revenue across five seasonal events, with 947% order growth over Black Friday Cyber Monday |
| ARRØ | Asked to double email revenue in 12 months | Email revenue grew 5.25x, from $21K to $110K, reaching $360,157.99 across email and SMS over two years |
| Metalbird | Seven Klaviyo accounts, seven currencies | One lifecycle system delivering 28.7% of revenue, with recipients up 119.4% on average and open rates up from 44.9% to 51.6% |
| Skinny Fizz | Almost no email presence at the start of the year | 921% increase in email revenue within 30 days |
| Puresport | Loyal supplement audience, basic lifecycle coverage | 354% increase in attributed revenue over six months, with layered campaigns and flows |
| Good & Fugly | Basic automations | 101% increase in email revenue within 18 days |
| Liquified RV | Email and SMS build over four months | $124,118.13 in email and SMS revenue, plus 15,629 new email subscribers and 10,334 new SMS subscribers |
| Canes Deer Velvet | No email strategy | $49,698.81 in attributable revenue, built from zero |
| Neat Feat | Three markets, one Klaviyo account | $39,052.62 in extra email revenue |
| Scott Hawaii | 92-year-old footwear brand | 121.6% year-on-year growth in email attributed revenue, without leaning harder on discounts |
The range matters as much as the size of the numbers. These brands sell footwear, skincare, candles, RVs, soft drinks, supplements and venison-derived products. The method stays the same: fix the account, build the flows, then scale. For a Black Friday example, see our BODYFX Black Friday case study.
Why In-box stands out among email marketing agencies
1. Klaviyo specialists, verified at the top tier
In-box works exclusively on Klaviyo, the platform most ecommerce brands use for email and SMS marketing. We are a Klaviyo Master Gold Partner, which reflects depth of platform expertise rather than general marketing knowledge. Every flow, template, segment and sign-up form is built natively in Klaviyo, so nothing is lost between a strategist and an outside developer. Our Klaviyo account set-up service covers new accounts and migrations.
2. Results shown through case studies, not promised
Most agencies describe outcomes in general terms. In-box publishes case studies with specific figures, timeframes and client context, so a prospective client can compare our work against their own goals before the first call. Our case study page is organised around three repeated steps: fix the foundations, build the flows that earn, then turn up the volume.
3. Coverage across the full lifecycle
Our services cover email campaigns, email automations, sign-up forms, SMS campaigns, Klaviyo account set-up and account audits. Many agencies handle one of these well. Brands that need the whole system, from first sign-up through to win-back, get it under one roof. Our email design portfolio shows the creative side of that work.
4. Strategy built from the brand's own data
We do not start with a template calendar. Our Klaviyo account audit looks at deliverability, list health, flow performance and segmentation before recommending changes. The same rigour applies to content: we design email header images that drive clicks, and we review standout creative so that tests are based on evidence rather than guesswork. You can also start with our free email audit docs.
5. Practical playbooks, shared openly
Our Insights library is written for ecommerce operators, not for search engines. It covers Klaviyo flow audits, sign-up form strategy for high-volume Shopify stores, why emails land in Gmail's Promotions tab and how to fix it, and how to read reporting for real store growth. Publishing this material lets prospective clients test our thinking before they hire us.
Recent guides from the In-box Insights library:
- Three 10-Minute Klaviyo Tweaks to Unlock Hidden Revenue
- How to Audit Your Klaviyo Flows Using Claude
- Why Your Emails Land in Promotions and How to Fix It
- What an Eight-Figure Store's Sign-Up Form Setup Looks Like
- 10 Questions to Ask Before Hiring a Klaviyo Agency
- How to Design Email Header Images That Drive Clicks
- Five Standout Email Designs and What to Steal from Them
- How to Build Emails from Figma into Klaviyo Faster
How to choose the best email marketing agency for your store
Whichever agency you consider, these checks will separate the strong from the weak:
- Ask for case studies with real figures. Look for named results, timeframes and the starting point. Compare ours in the In-box case studies.
- Confirm the platform specialism. A Klaviyo-focused agency will know the platform's data model, segmentation and reporting in depth.
- Ask how they start. A serious agency audits deliverability, list health and tracking before it proposes campaigns.
- Ask who does the work. You should know whether a founder or senior strategist is accountable for your account. Read our about page to see how In-box is run.
- Ask how results are reported. Revenue attribution, flow performance and list growth should be visible to you.
Our guide 10 Questions to Ask Before Hiring a Klaviyo Agency covers these in more detail and is a useful checklist regardless of which agency you choose. Our FAQ answers common questions about working with us.
Work with the best email marketing agency for ecommerce
In-box is a Klaviyo email and SMS agency for ecommerce brands. We build and run the flows, campaigns, sign-up forms and SMS programmes that turn email into a reliable revenue channel. If you want to see where your account is leaving revenue on the table, book a free audit and we will show you exactly where the opportunity sits. You can also explore our free email templates and weekly email inspiration.
Figures quoted are taken from In-box's published client case studies. Results depend on each account's starting point, product, and market.
