Every quarter, a marketing leader somewhere is building a business case to bring email in-house. The pitch usually looks like this: we're paying the agency £X per month. We could hire two people for that. We'd own the capability. We'd move faster.
The pitch is almost always wrong, and almost always for the same reasons. This post runs the actual numbers, the ones that don't appear in the job description or the agency invoice.
The model: what you're really comparing
To make this concrete, we'll use a mid-market D2C brand sending 400,000 emails per month across a managed programme: lifecycle flows, weekly campaigns, and a monthly strategy review. This is the profile where the in-house vs. agency debate is most active.
The three options are:
- Managed agency: full-service pod, strategist, copywriter, designer, developer, under a single monthly retainer.
- Senior in-house hire: one experienced email manager who designs and executes the programme, with internal copywriting support.
- In-house team: two or three hires covering strategy, copy, and design independently.
The agency cost: what you actually pay
A managed email programme for a 400k/month sender typically runs £6,000-£10,000 per month at a specialist direct-marketing agency, depending on programme complexity, number of active flows, and copy volume. We'll use £8,000/month, £96,000 per year.
Add your ESP cost (Klaviyo at this volume: ~£1,200/month; HubSpot Marketing Professional: ~£1,500/month). Let's use £1,200/month = £14,400/year.
Agency model total: £110,400/year.
What that gets you: a senior strategist reviewing cohort data monthly; a copywriter who's written for your specific category; a developer who knows your ESP's quirks; a designer who's built your brand into their workflow. And critically: a programme that runs when your internal team is sick, on holiday, or pulled onto something else.
The in-house cost: what people forget to include
The single-hire option sounds economical. A good senior email manager earns £55,000-£70,000 in the UK (or R600,000-R850,000 in South Africa). Let's use £62,000 base salary.
Add employer national insurance (13.8% on earnings over £9,100): £7,300.
Add pension contribution (minimum 3% of qualifying earnings): £1,500.
Add one month recruitment fee (standard agency charge is 15-20% of first-year salary): £9,300.
Add onboarding and training time, a new hire operates at 60-70% capacity for the first three months. On a £62k salary basis, that's roughly £5,200 in productivity cost.
Add hardware, software licences (Figma, Litmus, project management), and communication tools: £2,400/year.
Single hire year-one total: £87,700, before ESP costs.
Add ESP: £87,700 + £14,400 = £102,100/year.
That's cheaper than the agency, by about £8,000. But we haven't added the hidden costs yet.
The hidden costs that make in-house more expensive
1. The capability gap
A single email manager can execute, they cannot simultaneously be a world-class copywriter, a Klaviyo developer, a designer, and a strategist who's monitoring deliverability at 11pm on a campaign night. The work they can't do falls one of two ways: it doesn't get done, or it gets contracted out.
The programmes that consistently underperform are the ones with a single in-house operator managing breadth instead of depth. "Good at copy, average at design" programmes leak revenue on design quality. "Good at design, thin on strategy" programmes miss the cohort signals that a dedicated strategist would catch.
Budget conservatively £1,500/month for freelance copywriting top-up, or accept the capability gap. We'll add it: £18,000/year.
2. Attrition and re-hire risk
The average tenure of a senior email marketer in 2024 is 18-24 months. When they leave, and in a hot market, they will, you pay the recruitment fee again, lose 3-6 months of programme momentum during handover and ramp, and start the training clock over.
On a 24-month tenure assumption, the annualised cost of attrition (re-recruitment + ramp loss) is approximately £7,200/year, and that's optimistic. Add it.
3. Management overhead
An in-house email hire doesn't manage themselves. Someone senior reviews briefs, approves campaigns, handles performance conversations, and ensures the strategy aligns with the commercial plan. At even 10% of a Head of Marketing's time (£80,000 salary), that's £8,000/year in management cost that wouldn't exist with an agency managing its own output.
4. Deliverability recovery cost
Domain reputation issues happen. When they do, an agency with a dedicated deliverability practice resolves them within 48 hours. An in-house email manager typically doesn't have the tooling or the institutional knowledge, meaning you're either buying in a consultant (£200-400/day) or accepting weeks of degraded placement while your hire figures it out.
This is an infrequent but high-impact cost. Budget £3,000/year as a contingency, it usually isn't needed, but when it is, it dwarfs a month's agency retainer.
The real single-hire total (year one)
Base: £87,700 + ESP: £14,400 + freelance copy top-up: £18,000 + attrition annualised: £7,200 + management overhead: £8,000 + deliverability contingency: £3,000 = £138,300/year.
That's £27,900 more than the managed agency, before considering the speed advantage of a fully-ramped team that starts delivering on day one.
The in-house team model (3 hires)
If you're going all-in, strategist, copywriter, designer, the maths shifts. A small in-house team with genuine depth can outperform an agency on brand consistency and speed of execution once it's established. The cost picture changes too.
Three mid-level hires at an average £48,000 each: £144,000 in salary. Employer NI: £17,400. Pensions: £4,300. Recruitment (three fees at 15%): £21,600. First-year onboarding gap: £9,000. Tools and hardware: £5,000.
Three-hire year-one total: £201,300 + ESP: £14,400 = £215,700/year.
By year two, the recruitment and onboarding costs fall away. The steady-state annual cost settles at approximately £168,000, still 52% more expensive than the managed agency. The break-even requires either significant volume growth (to the point where the agency can't scale without charging more) or a programme scope that genuinely requires full-time attention across all three disciplines simultaneously.
When in-house genuinely wins
The model breaks the other way in specific conditions:
- Volume above 2 million sends per month. At this scale, the agency's time-per-send ratio starts to produce meaningful savings from a dedicated team, especially if the programme has high complexity and requires daily iteration.
- Highly regulated industries. Fintech and pharma programmes with intense compliance requirements often benefit from in-house ownership, where legal review and send approval sit inside the same team.
- Existing strong creative team. If you already have a senior designer and copywriter who can absorb email as 30% of their role, the marginal cost of adding an email strategist is genuinely lower than a full managed service.
- Product-led growth models. Brands where email is tightly integrated with product events (SaaS, fintech) often need engineering-adjacent email operations that agencies struggle to serve efficiently.
The honest version of this decision
Most brands choosing between managed and in-house are really asking a different question: do we trust an agency to understand our brand well enough, or do we need that ownership inside the team?
That's a legitimate concern, and it's one a well-run agency should be able to answer with track record, not promises. The financial case for in-house is almost never as strong as it looks at first. But if the trust and brand alignment question doesn't have a good answer, no cost model will fix it.
Run the real numbers. Add the hidden costs. Then make the decision on trust.