From Founder Sends to a Repeatable SaaS Outbound Motion
There's a moment in every SaaS company's life when outbound stops being something the founder does between meetings and becomes a system the company runs. The first SDR gets hired, pipeline targets get a number attached, and ad-hoc sends have to give way to capacity planning: how many emails per day do we need, how many mailboxes does that take, and who owns the experiments that improve reply rates quarter over quarter?
Instantly is a strong sequencing layer for exactly this transition — unlimited email accounts on paid plans, bulk account import, A/Z variant testing, and campaign analytics built for teams that iterate. What it doesn't provide is the sending infrastructure itself. This guide covers how growth-stage SaaS teams pair Instantly with ColdRelay — provisioning the mailbox pool, importing it in bulk, and building the capacity model that lets outbound scale with headcount instead of breaking under it.
Why Run Instantly on ColdRelay Infrastructure
Instantly handles campaigns, account rotation, variant testing, and replies in the Unibox — but it sends from whatever mailboxes you bring. When you're moving from founder-led sends to an SDR team, that detail becomes the whole ballgame: a motion that needs 200+ outbound emails a day can't run on a handful of hand-built Google Workspace seats, and it absolutely can't run on your product domain.
ColdRelay supplies the layer underneath. Mailboxes provision on isolated Azure tenants with dedicated IPs, DNS (SPF, DKIM, DMARC) pre-configured, ready in about an hour — and because warmup runs continuously as part of each mailbox's daily budget, there's no warmup waiting period before your SDRs start sending. Each mailbox sends 4 emails/day total — 2 outbound + 2 warmup — which makes capacity math trivially predictable for planning.
The economics of the pairing favor scaling teams specifically. Instantly's unlimited-accounts model means your software bill doesn't move when you grow the pool from 50 mailboxes to 300; only the infrastructure line scales, and ColdRelay's volume tiers reward exactly that growth. ColdRelay is the infrastructure layer, Instantly is the sending layer on top — additive, not competitive.
Visit Instantly →Connecting ColdRelay Mailboxes to Instantly at Team Scale
Size the pool from your pipeline math, then provision
Work backwards from targets: if each SDR needs 100 outbound sends/day, that's 50 mailboxes per rep at 2 outbound sends/day each (4/day total including 2 warmup). A two-SDR team typically provisions 100-150 mailboxes — which fits on a single secondary domain, since ColdRelay supports 100-150 mailboxes per domain. Everything spins up on isolated Azure tenants with dedicated IPs in about an hour, DNS pre-configured.
Export the full pool as CSV from ColdRelay
Export the mailbox list with SMTP/IMAP credentials from the ColdRelay dashboard in one file. The CSV column layout matches what Instantly's bulk importer expects, so a 150-mailbox pool moves over in one upload instead of 150 manual connections.
Bulk-import via Instantly's SMTP/IMAP CSV upload
In Instantly, go to Email Accounts → Add New → Bulk Import (SMTP/IMAP) and upload the CSV. Paid Instantly plans allow unlimited email accounts, so the entire pool connects under your existing subscription — and the next 100 mailboxes you add as the team grows cost nothing extra on the software side.
Bulk-set daily limits and skip Instantly's warmup pool
Use Instantly's bulk account settings to cap each mailbox at 2 campaign emails per day, mirroring ColdRelay's budget of 4 sends/day total — 2 outbound + 2 warmup. Leave Instantly's warmup pool disabled for these accounts; ColdRelay's continuous warmup already fills the other half of the budget, and double-warming just burns capacity.
Launch campaigns with A/Z variants and assign Unibox ownership
Build campaigns in Instantly with multiple subject and body variants — A/Z testing, not just A/B — and attach the full mailbox pool so sends rotate evenly. Route each campaign's replies to a named owner in the Unibox: once outbound is a team motion, an unowned reply queue is where pipeline goes to die.
The Growth-Stage SaaS Instantly Playbook
Make capacity a planning number, not a guess
Because every ColdRelay mailbox sends exactly 2 outbound emails/day (4/day total with 2 warmup), outbound capacity becomes a spreadsheet cell: mailboxes × 2 = daily sends. Plan mailbox provisioning one hiring cycle ahead, so infrastructure is live before the new SDR's first day instead of after.
Run A/Z tests like the growth team runs experiments
Treat Instantly's variant testing as part of the company's experiment loop, not an SDR side project. Test one variable at a time across 4-6 variants, set a minimum send threshold before declaring winners, and log results where the growth team logs everything else. Reply rate by variant is a growth metric.
Standardize sequences before you scale headcount
The founder's instincts don't transfer by osmosis. Before SDR two joins, codify what worked into named Instantly campaign templates — persona, problem framing, CTA, follow-up cadence — so new reps inherit a tested playbook and their numbers are comparable to it.
Keep product email and outbound on separate rails
Trials, onboarding, billing, and password resets live on your primary domain; every cold sequence lives on ColdRelay secondary domains connected to Instantly. As volume scales into the hundreds of sends per day, this separation is what keeps an aggressive quarter of outbound from ever touching product deliverability.
Typical Growth-Stage SaaS Benchmarks (Instantly + ColdRelay)
| Metric | Benchmark | Notes |
|---|---|---|
| Inbox placement rate | 95%+ | Dedicated IPs and isolated tenants outperform shared Google/Microsoft pools |
| Reply rate | 2-5% | Templated team sequences land below founder-signed rates; A/Z testing claws it back |
| Outbound capacity per mailbox | 2/day | 4 sends/day total per mailbox — 2 outbound + 2 warmup |
| Mailboxes per SDR | 50-75 | 100-150 outbound sends/day per rep; one ColdRelay domain covers a rep's full pool |
| Time from provisioning to live campaign | Same day | ~60 minutes on ColdRelay, plus bulk import and campaign setup in Instantly |
What It Costs: Instantly + ColdRelay
Infrastructure is priced per mailbox per month, with volume tiers that drop as the pool grows (see the table below) — so the per-unit cost falls exactly when a scaling team's mailbox count rises. DNS, dedicated IPs, and isolated Azure tenants are included.
Instantly is billed separately on its own subscription. Unlimited email accounts on paid plans mean the software line stays flat whether you connect 50 ColdRelay mailboxes or 500 — there's no per-seat sending cost to model into headcount plans.
For a team budgeting outbound as a channel, the math is clean: software is a fixed cost, infrastructure scales linearly with capacity, and capacity scales linearly with SDR headcount. Cost per outbound send is knowable before the quarter starts.
| Mailboxes | ColdRelay price / mailbox / month |
|---|---|
| 1–199 | $1.00 |
| 200–999 | $0.85 |
| 1,000–4,999 | $0.70 |
| 5,000+ | $0.55 |
Each mailbox sends 4 emails per day — 2 outbound to prospects + 2 warmup. ColdRelay provisions mailboxes on isolated Azure tenants with dedicated IPs; Instantly handles the sending, sequencing, and inbox rotation on top.
Frequently Asked Questions
Is ColdRelay an alternative to Instantly?
No — they sit at different layers of the same stack and are used together. Instantly is the sending layer: campaigns, A/Z testing, account rotation, and the Unibox. ColdRelay is the infrastructure layer underneath: the secondary domains, mailboxes, and dedicated IPs that Instantly sends from. Neither replaces the other.
How do we plan mailbox capacity for our first SDR hires?
Use the per-mailbox budget as the unit: each ColdRelay mailbox sends 4 emails/day total — 2 outbound + 2 warmup — so every 50 mailboxes is 100 outbound sends/day. Most growth-stage teams allocate 50-75 mailboxes per SDR and provision the pool before the rep starts. Since ColdRelay supports 100-150 mailboxes per domain and Instantly allows unlimited accounts, adding a rep's worth of capacity is an ordering decision, not an architecture change.
Does scaling the mailbox pool increase our Instantly bill?
No. Paid Instantly plans include unlimited email accounts, so connecting more ColdRelay mailboxes via the bulk SMTP/IMAP CSV import doesn't change the software cost. The only line that scales with capacity is infrastructure — and ColdRelay's volume tiers lower the per-mailbox rate as the pool grows.
Do new mailboxes need a warmup period before SDRs can send from them?
No waiting period. ColdRelay mailboxes warm continuously — 2 warmup sends/day per mailbox as part of the 4/day budget — so a pool provisioned in about an hour can carry live campaigns the same day. Keep Instantly's own warmup pool disabled for these accounts and point Instantly at outbound sending only.