This list is for ecommerce founders and marketing leads who want an outside team to run email and SMS. Maybe your flows have not been touched in a year, your campaigns go out late, or you are moving to Klaviyo, Omnisend, Attentive or Postscript and want help doing it properly. Every agency here focuses on retention for online stores, not general digital marketing.
Use the quick comparison table to shortlist two or three names, then read the full entries for the details that matter to you: platform depth, the size of brand each one targets, and how they charge. We only included facts we could confirm on each agency's own website or its Klaviyo partner directory listing in October 2026.
Quick note before the list: this is our list, so yes, GrowwithBA sits at #1. We say why below, and you can weigh that yourself. The other nine are firms we would happily point a brand to, and nobody paid to be here.
How we chose
- Retention focus. Email and SMS for ecommerce must be a core service, not an add-on buried in a long menu.
- Platform depth. Proven work in Klaviyo, and ideally experience with Attentive, Postscript, Omnisend or other tools DTC brands actually use.
- Verifiable information. Services, location and results had to be published on the agency's own site or an official partner directory we opened.
- Clear fit. Each agency states the type or size of brand it works best with, so you can tell quickly if you are a match.
- Full lifecycle work. Flows, campaigns, segmentation, list growth and deliverability, not only email design.
- Currently operating. Live website, active offers and recent work. We removed one well-known agency whose site was offline when we checked.
Quick comparison
| Rank | Company | Best for | HQ | Pricing info |
|---|---|---|---|---|
| 1 | GrowwithBA | Ecommerce brands that want email and SMS planned together with paid ads and CRO | Nagpur, India and Dover, DE, USA | Published on site (from $1,500/mo for SEO or ads) |
| #2 | Chronos Agency | Scaling DTC brands that want email, SMS and push run by a top-tier Klaviyo partner | Sydney, Australia (also lists a Singapore address) | Not published |
| #3 | Flowium | Klaviyo-first brands that want a wide channel mix, including WhatsApp, RCS and direct mail | North America (city not stated on site) | Not published; site advertises no long-term contracts and a 2-year price lock |
| #4 | Andzen | Brands selling across APAC, North America and Europe that need Klaviyo plus a broader CRM stack | South Brisbane, Australia | Not published; retainer, project and hourly options |
| #5 | Hustler Marketing | Ecommerce brands that want a dedicated four-person email and SMS team | Jackson, Wyoming, USA | Not published; one-time flow build plus monthly retainer |
| #6 | The Email Marketers | 8-figure DTC brands, including VC or PE backed ones, that want month-to-month retention support | Santa Monica (Los Angeles), California, USA | Not published; client example cites a $4,500/month retainer |
| #7 | Sticky Digital | Shopify brands that want retention and tech stack cleanup handled together | Not stated on site | Not published; free audit offered |
| #8 | Darkroom | $10M+ brands that want retention run alongside paid media, Amazon and retail | New York, New York, USA | Not published |
| #9 | Sweat Pants Agency | Subscription and DTC brands doing $1M+ that want senior-only email and SMS support | Nashville, Tennessee, USA (remote team) | Not published; month-to-month, no setup fees |
| #10 | InboxArmy | Brands on less common or enterprise ESPs, and agencies that need white-label email help | Grapevine, Texas, USA | From $1,500/month (stated minimum) |
The list
#1. GrowwithBA
GrowwithBA is the agency brand of Bridging Associates, with offices in Nagpur, India and Dover, Delaware, USA. Engagements are senior-led and start with a free growth audit, and the team ends engagements that are not moving revenue.
Best for: D2C brands that want retention planned with acquisition, not in a separate silo.
What stands out:
- Email and retention and subscription retention services for Klaviyo-style stacks.
- The same team runs paid ads and CRO, so flows, offers and landing pages line up.
- Free email list value and Klaviyo flow audit tools.
Worth knowing: GrowwithBA is a full-funnel agency, not an email-only shop; brands that want a pure retention specialist should compare the specialists below.
#2. Chronos Agency
Chronos Agency is a retention and lifecycle agency for DTC brands. It says it has worked with more than 500 DTC brands since 2017 and lists offices in Sydney and Singapore.
Best for: Scaling DTC brands that want email, SMS and push run by a top-tier Klaviyo partner.
What stands out:
- Shown as an Elite Master partner on its Klaviyo partner directory listing, which the agency describes as Klaviyo's highest service partner tier.
- Covers email, SMS, push, WhatsApp, RCS and direct mail, with Klaviyo audits, migrations and onboarding.
- Publishes named client results in its directory listing, including The Oodie, Garvee, Fenix and Organifi.
- Its homepage reports more than $400M in attributable revenue generated for clients.
Worth knowing:
- Pricing is not published, so you need a strategy call for a quote.
- Its Klaviyo listing targets brands from $10M to $500M in annual revenue, so very small stores may not be the focus.
#3. Flowium
Flowium is a retention marketing agency for ecommerce brands. Its about page says it was founded in 2017, originally as Email Marketing NYC, and its homepage says it has worked with 1,000+ brands since then.
Best for: Klaviyo-first brands that want a wide channel mix, including WhatsApp, RCS and direct mail.
What stands out:
- Listed as an Elite Master partner in the Klaviyo partner directory.
- Offers more channels than most: email, SMS, push, WhatsApp, RCS, Instagram DM automation and direct mail.
- Runs a free lifecycle diagnosis and publishes industry case studies, an email showcase and the Email Einstein podcast.
- Its homepage lists no long-term contracts and a two-year price lock guarantee.
Worth knowing:
- Exact prices are not listed on the site.
- Its directory listing covers North America only as a service region.
#4. Andzen
Andzen calls itself a customer journey and AI CRM agency for ecommerce. Its contact page lists an office in South Brisbane, and it says it has teams in North America, Europe and Australia.
Best for: Brands selling across APAC, North America and Europe that need Klaviyo plus a broader CRM stack.
What stands out:
- Listed as Elite Master in the Klaviyo partner directory. Andzen says it was the first Elite Master partner in APAC and the fifth worldwide.
- Works across a wide stack, including SMS tools such as Postscript, loyalty, reviews, subscriptions and helpdesk platforms.
- Its directory listing offers retainer, one-time project and hourly consulting options, and covers brands from $1M to over $500M in revenue.
- Supports clients in English, German and Spanish.
Worth knowing:
- Pricing is not published.
- The wide platform menu suits brands with complex stacks; a small store that only needs a few flows may not need that breadth.
#5. Hustler Marketing
Hustler Marketing offers fully managed email and SMS for ecommerce stores, plus UGC ad creative and CRM setup and migration. Its site lists an address in Jackson, Wyoming.
Best for: Ecommerce brands that want a dedicated four-person email and SMS team.
What stands out:
- Listed as Elite Master in the Klaviyo partner directory.
- Each client gets a four-person team: account manager, designer, copywriter and technical specialist.
- Its directory listing says each account manager handles only two or three stores.
- Client work shown in its listing includes BlendJet and TAO Clean.
Worth knowing:
- Rates are not disclosed. The site says flows are a one-time investment and campaigns run on a monthly retainer.
- We could not find a dedicated contact page; enquiries go through its free call booking.
#6. The Email Marketers
The Email Marketers is a retention agency founded in 2020 by Melanie Balke. Its about page says it is based in Santa Monica, California, with a fully remote, US-led team.
Best for: 8-figure DTC brands, including VC or PE backed ones, that want month-to-month retention support.
What stands out:
- Listed as Platinum Master in the Klaviyo partner directory.
- Covers email, SMS, direct mail, subscriptions, memberships, referral and loyalty programs.
- Says its sweet spot is 8-figure brands and that it often works with VC or private equity backed companies.
- Publishes a dated case study for Koala Eco in Australia and the US, including the retainer amount.
Worth knowing:
- No standard price list. The Koala Eco example mentions a $4,500 per month retainer, which gives a rough sense of scale.
- Brands well below 8 figures may find they are not the core target.
#7. Sticky Digital
Sticky Digital describes itself as Shopify's premier retention agency. It focuses on email, SMS, loyalty, subscriptions and Shopify tech stack optimization.
Best for: Shopify brands that want retention and tech stack cleanup handled together.
What stands out:
- Listed as Platinum Master in the Klaviyo partner directory.
- Bases recommendations on RFM analysis and says it A/B tests every retention tactic it uses.
- Offers a free retention audit and complimentary Klaviyo migrations.
- Also does conversion rate optimization and app stack cleanup on Shopify.
Worth knowing:
- Its headquarters city and pricing are not stated on the site.
- It is strongly Shopify focused, so brands on other platforms should confirm fit early.
#8. Darkroom
Darkroom is a New York growth agency with a dedicated retention service. It is the most full-service option on this list.
Best for: $10M+ brands that want retention run alongside paid media, Amazon and retail.
What stands out:
- Its retention page says it builds inside Klaviyo, Attentive, Postscript, Yotpo and Recharge.
- Retention scope includes a customer journey map, lifecycle automations, monthly email and SMS campaigns and loyalty program design.
- Its homepage cites Morphe growing retention revenue 75% year over year.
- Can combine retention with Amazon, retail media and paid social under one team.
Worth knowing:
- Darkroom says it is a poor fit for single-channel brands and companies under roughly $5M; its typical clients are $10M to $500M.
- Pricing is not published.
#9. Sweat Pants Agency
Sweat Pants Agency is a performance agency for DTC and subscription brands with a large email and SMS practice. Its site lists Nashville, Tennessee, with a remote team.
Best for: Subscription and DTC brands doing $1M+ that want senior-only email and SMS support.
What stands out:
- Listed as Silver Master in the Klaviyo partner directory.
- Says it has sent over 4.3 billion emails and 147 million SMS messages, and pioneered in-cycle upsells for subscription brands.
- Its pricing page explains month-to-month contracts with no setup fees.
- Its directory listing names clients such as Hunt A Killer, SugarWish and Bokksu.
Worth knowing:
- It does not publish specific prices; scope depends on how many emails and SMS you send. Its pricing page says it suits brands doing $1M+.
- It also sells paid media, so confirm you are getting a retention-focused team.
#10. InboxArmy
InboxArmy is an email and SMS agency founded in 2016, with an address in Grapevine, Texas. It says it only does email and SMS, with no SEO, social or PPC upsells.
Best for: Brands on less common or enterprise ESPs, and agencies that need white-label email help.
What stands out:
- Supports 40+ email platforms, including Klaviyo, Omnisend, Salesforce Marketing Cloud, Braze and Iterable.
- Assigns an account director who knows your industry and your platform.
- Offers white-label email services for agencies as well as direct work for brands.
- Says it has worked with 5,000+ brands across 25 industries, including ecommerce.
Worth knowing:
- Its stated minimum for monthly managed services is $1,500 per month.
- It serves many industries beyond ecommerce, so ask for DTC-specific examples.
How to choose
Before you sign, ask each shortlisted agency these questions. Good answers are specific, not generic.
- Which platforms do you run every day? If you are on Attentive, Postscript or Omnisend, ask for live examples on that tool, not just Klaviyo. Our guide to the best email platform for DTC brands can help you decide whether a migration makes sense first.
- Who works on my account? Get names and roles, and ask how many other brands each person handles.
- How do you measure success? Ask how they report revenue, and whether they look at repeat purchase rate and customer lifetime value rather than open rates alone. For context on what normal looks like, see our email open rate benchmarks for 2026.
- What happens in the first 90 days? A good agency will describe an audit, a flow rebuild order and a campaign calendar.
- How do you handle deliverability and SMS compliance? Ask about list hygiene, sending domains and SMS consent rules.
- What are the contract terms? Check minimum terms, notice periods, setup fees and who owns the templates and flows if you leave.
- What is my list actually worth? Run your numbers through our email list value calculator so you can judge whether a retainer will pay for itself.
FAQ
What does an ecommerce email and SMS agency do?
It plans, builds and runs your owned channels. That usually means automated flows such as welcome, abandoned cart, post-purchase and win-back, plus a monthly campaign calendar, segmentation, list growth forms and deliverability work. Many also handle SMS, loyalty and subscription messaging.
Do I need Klaviyo to work with these agencies?
No. Klaviyo is the most common platform among the agencies on this list, but several also work in Attentive, Postscript, Omnisend and other tools. InboxArmy, for example, says it supports more than 40 email platforms. Always ask for examples on your exact platform.
How much do email and SMS agencies cost?
Most agencies on this list do not publish fixed prices. Of those that share numbers, InboxArmy states a $1,500 per month minimum and The Email Marketers cites a client on a $4,500 per month retainer. Expect quotes to depend on how many campaigns and flows you need. If you are weighing this against a broader program, our email and retention service page explains how we scope it.
Is SMS worth it for a subscription brand?
It can be, because subscription brands have clear moments to message, such as upcoming renewals, skips and in-cycle upsells. Make sure your agency understands consent rules and your subscription app. See our subscription retention service for how we approach it.
Method note: we checked each agency's website, and its Klaviyo partner directory listing where one exists, in October 2026. Partner tiers are shown only where we saw them on the directory listing. Spotted an error? Email partner@growwithba.com.