Email marketing for agencies, priced per client domain

Run four client newsletters on Mailchimp Essentials at 500, 1,000, 5,000, and 10,000 contacts and the bill is $224.50 a month against Mailchimp's verified August 2026 tiers. That is this month's number. Next month a client runs a good campaign, crosses a tier boundary, and it changes without anyone deciding anything. Your retainer was signed in January.

The ratchets differ by vendor and point the same way. Mailchimp counts subscribed, unsubscribed, and non-subscribed contacts toward the billable total and archives nobody automatically, so you pay for a client's dead addresses until an account manager remembers to clean them. Klaviyo went further on February 18, 2025: plan tiers now have to match the active profile count, paid accounts upgrade themselves at the next billing cycle, and Klaviyo publishes no annual discount at all, so there is no prepay lever to soften it. Constant Contact's Lite plan goes from $12 to $30 the moment a client passes 500 contacts.

Then the caps only agencies hit. Mailchimp Essentials includes 3 seats, Standard 5. Brevo's Standard plan tops out at 3 marketing seats and charges $12 a month for each one after. beehiiv's Scale plan allows 3 publications, so client number four means the Max plan at $109 a month or more. You end up buying a plan per client, or explaining why their newsletter shares a login with a competitor's.

What LetterDuck replaces

What email marketing for agencies actually costs

Public list prices, August 2026, annual billing where offered. Mailchimp: Essentials on monthly billing, the cheapest paid tier. Standard runs $20 to $135 across the same contact counts. First-year promotional discounts are excluded. Klaviyo: Email plan, billed by active profile count. Klaviyo publishes no annual discount on self-serve plans, so monthly is the effective price. LetterDuck is $50 per domain, flat, unlimited addresses and subscribers.

Now put a real roster against it. Four clients, four list sizes, using the verified August 2026 tier prices for each vendor's cheapest sensible paid plan.

Two things there matter more than the totals. Your small clients are cheaper elsewhere and we say so: at 500 contacts Mailchimp is $13 and we are $50. And the left-hand columns are a forecast rather than a price, because every one of them moves when a client's list moves, which drifts the input cost on a fixed-fee retainer in exactly the direction that hurts. A flat per-domain rate makes the pass-through line identical in month one and month thirty.

Mailchimp and Klaviyo are also outbound-only, which is why the roster needs that mailbox row. Campaign replies, unsubscribe complaints, and the "is this really from you?" question all arrive somewhere, and on most rosters that somewhere is one person's mailbox. Here every address on the client's domain feeds one threaded shared inbox, and anyone on the account team replies as the address the thread belongs to.

Deliverability you can put on the invoice

The technical half of email marketing is the half clients cannot evaluate and will not pay for by the hour. It is also the half that decides whether the campaign existed at all. Gmail started rejecting unauthenticated mail outright in November 2025 and Microsoft did the same in May 2025, so SPF, DKIM, and DMARC are a gate rather than a scoring factor. Under Google's bulk-sender rules, a client whose spam-complaint rate reaches 0.3 percent loses delivery mitigation until they hold under 0.3 percent for seven consecutive days.

On every client domain the same controls run without anyone remembering them: authentication records generated and checked, a warm-up ramp starting near 150 sends on day one and reaching about 1,100 a day by day seven, growth capped at 10 to 20 percent a day while complaints stay under 0.1 percent and bounces under 2 percent, an automatic halt at 0.3 percent complaints or 2 percent bounces, a per-client suppression list checked before every single send, a Feedback-ID on each message, and RFC 8058 one-click unsubscribe on every campaign.

That list is a service description. Bill it as managed deliverability, or fold it into the retainer and stop absorbing the risk quietly. The client-facing version is our deliverability playbook, and why the spam-complaint rate is the number that matters is what to send when a client asks why volume is capped.

Handover, and who owns what

The reputation you build belongs to the client's domain, not to a platform's shared pool. Say that out loud in a pitch: if the relationship ends, the client keeps the domain, the DNS records, the contact list, and the opt-out history, and none of it needs your permission to keep working. Their domain reputation is an asset you built for them, which is a better story than "we will export a CSV."

It cuts both ways, and we would rather be honest than lock a roster in. Practically, warm-up is per domain and takes weeks, so onboard a client's sending domain before the campaign calendar needs it; the setup path is the one in our business email setup guide. The part clients underestimate is that reputation matures over four to eight weeks no matter how good the copy is.

Which agencies should not pick LetterDuck

If your deliverable is revenue attribution, buy Klaviyo. Storefront integrations, predictive analytics, and flows tied to purchase events are things we do not attempt, and an ecommerce agency without them works with one hand tied. Same answer for lifecycle shops running 200-step journeys in Mailchimp, which LetterDuck vs Mailchimp lays out in full.

Three more limits, stated plainly. Each client domain is its own workspace and its own $50 line, so there is no cross-client rollup dashboard, no white-label branding, and no reseller billing today. If unlimited seats on one shared marketing account is the shape you want, MailerLite's Power plan is exactly that and cheaper at small list sizes. And LetterDuck is in waitlist mode, so this is a place in line rather than an account you provision this afternoon.