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SDR tech stack guide 2026: what each tool does, how they connect, total cost, and the exact configuration that turns a stack into a system.
Marcus Chen
Outbound sales consultant, 12+ years in SDR leadership · Updated June 24, 2026
Last updated: June 2026 · Marcus Chen, outbound sales consultant, 12+ years in SDR leadership
TL;DR — 7 things to know before reading
Most SDR stack guides are lists of tools in categories. This guide covers the SDR stack as a system: four layers, each with a defined function, and defined connections between them. Understanding the connections between layers is as important as understanding the layers themselves — a great email sequencing tool configured with bad contact data will produce bad results regardless of its feature set.
The unique angle of this guide is tool selection from a system integration perspective. When choosing an SDR tool in any layer, the most important question is not "what are its features?" but "how does the data produced by this tool flow to the next layer, and what can break at that handoff?" The handoff points between layers are where most SDR stack failures occur.
Function: Identifies and delivers the verified contact records (name, job title, company, email) that all downstream outreach is directed at.
Tool: Quarvio
Why this layer matters: The contact data layer is the source layer for the entire stack. Every email sent, every LinkedIn connection request made, every meeting booked — all depend on the contact data in Layer 1. A contact data layer that delivers 5% invalid emails produces a bounce rate that damages infrastructure (Layer 2) before the sequence (Layer 3) gets a chance to run.
Quarvio delivers pre-verified B2B contact data filtered by job title, company size, and industry. The SMTP verification is completed before delivery, meaning contacts imported to Layer 3 (Instantly) are ready for immediate use without a separate verification step.
Key feature for SDRs: ICP filtering. The ICP (Ideal Customer Profile) definition lives in Layer 1. Quarvio allows filtering by job title, seniority level, company size, and industry. The specificity of the filter directly determines the quality of the contact list and, downstream, the reply rate of the sequence.
| Package | Contacts | Price | Cost per contact |
|---|---|---|---|
| Starter | 5,000 | $129 | $0.026 |
| Growth | 10,000 | $199 | $0.020 |
| Scale | 25,000 | $399 | $0.016 |
| Pro | 50,000 | $699 | $0.014 |
All packages: one-time purchase, credits valid for 12 months, unused credits returned if unused at expiry.
Quarvio delivers contacts in CSV format with the following fields: First name, Last name, Email, Job title, Company, Company size, Industry, Location. All fields are required for sequence personalisation; verify that all fields are populated before importing to Layer 3.
The handoff from Layer 1 (contact data) to Layer 3 (sequencing) is via CSV import in Instantly. Before import: (1) cross-check contacts against the suppression list to remove previously contacted addresses, (2) segment contacts by ICP sub-variant if running multiple campaigns, (3) verify all personalisation fields are populated.
Function: Provides the sending inboxes, domains, and DNS authentication required to deliver cold email to prospect inboxes at scale without damaging the primary company domain.
Tool: Inframail
Why this layer matters: Without dedicated sending infrastructure, cold email volume lands in spam (Google Workspace personal plans flag high-volume cold email) or the primary company domain reputation is damaged by spam complaints (making all company email — marketing, transactional, internal — less deliverable).
Inframail provisions Microsoft 365 mailboxes on dedicated cold email domains with automated SPF, DKIM, and DMARC configuration. Each domain is a separate sending identity from the primary company domain, isolating cold email reputation from all other company email.
Key feature for SDRs: flat-rate inbox pricing. Most alternatives price per inbox per month. Inframail's flat rate makes scaling from 5 inboxes to 50 inboxes economically viable without a proportional cost increase.
| SDR target sends/day | Inboxes needed (at 40/inbox/day) | Domains needed (3 per domain) |
|---|---|---|
| 100 | 3 | 1 |
| 200 | 5 | 2 |
| 300 | 8 | 3 |
| 500 | 13 | 5 |
| 1,000 | 25 | 9 |
Per Woodpecker's warmup guide: every new inbox requires 2–4 weeks of warmup before any production sends. "Warmup" means the inbox is engaging in low-volume email exchanges (typically with other warmed inboxes via an AI warmup tool) to build a send history and reputation with email providers before receiving cold email instructions.
Inframail supports AI-enabled warmup integration. Warmup must be enabled on all inboxes immediately after provisioning, before any campaign sends.
Layer 2 (Inframail inboxes) connects to Layer 3 (Instantly) via IMAP/SMTP or direct OAuth integration. In Instantly, each Inframail inbox is added as a separate sending account. Instantly then distributes sends across all connected inboxes via inbox rotation (different contacts receive emails from different inboxes, preventing any single inbox from exceeding its daily send limit).
Critical check at Layer 2–3 connection: Verify that all connected inboxes in Instantly show domain reputation "High" in Google Postmaster Tools before enabling any production sends. Sending from "Low" reputation inboxes in a campaign delivers to spam even with good copy.
Function: Manages the schedule, personalisation, sequencing, and reply tracking of all outbound email outreach.
Tool: Instantly
Why this layer matters: Layer 3 is the execution layer. The quality of the contact data (Layer 1) and the health of the infrastructure (Layer 2) determine the ceiling of what Layer 3 can achieve; Layer 3 determines how much of that ceiling is actually reached via sequence structure, personalisation, timing, and follow-up cadence.
Instantly provides: campaign management (import contacts, assign to sequence, set schedule), inbox rotation (sends distributed across all connected inboxes), sequence builder (multi-step email sequences with personalisation variables), Unibox (unified reply inbox for all connected accounts), analytics (open rate, reply rate, bounce rate per campaign), and A/B testing.
Key feature for SDRs: Unibox. At any meaningful send volume (50+ sends/day), replies from multiple inboxes and campaigns become difficult to manage individually. Unibox consolidates all replies across all connected inboxes into a single view with labelling (Interested, Not interested, Not now, Referral, Out of office), enabling reply management without switching between inbox accounts.
| Step | Timing | Purpose | Target length |
|---|---|---|---|
| Email 1 | Day 1 | Specific problem + proof + CTA | Under 100 words |
| Email 2 | Day 4 | Different angle or additional evidence | Under 80 words |
| Email 3 | Day 8 | Social proof or case reference | Under 80 words |
| Email 4 | Day 14 | Break-up with open invitation | Under 60 words |
Per Instantly's 2026 benchmark report: average reply rate across all senders is 3.43%; elite senders (above 10% reply rate) distinguish themselves primarily by ICP precision and personalised first-line copy, not by sequence length or timing.
| Plan | Price/month | Inboxes | Contacts |
|---|---|---|---|
| Growth | $30 | Unlimited | 1,000 active |
| Hypergrowth | $77.60 | Unlimited | 25,000 active |
For most SDR setups, Growth starts sufficient and Hypergrowth becomes appropriate at 5,000+ contacts in active campaigns.
Layer 3 (Instantly) connects to Layer 4 (Aimfox/LinkedIn) via manual coordination: the same contacts in an active Instantly campaign are also added to an Aimfox LinkedIn sequence, timed to touch via LinkedIn 2–3 days after the Email 1 send in Instantly.
The Layer 3–4 connection is the most manual handoff in the stack. Some teams manage it by exporting the campaign contact list from Instantly and importing to Aimfox; others maintain a shared contact list that feeds both tools simultaneously.
Function: Delivers parallel LinkedIn touchpoints to the same ICP contacts as the email sequence, increasing total reply rate through multichannel presence.
Tool: Aimfox
Why this layer matters: Per Woodpecker's research, email + LinkedIn multichannel outreach increases total reply rate by 40–60% compared to email alone. This improvement comes from two mechanisms: (1) the LinkedIn connection creates a visibility signal before the email sequence continues, and (2) the LinkedIn touchpoint reaches prospects who prefer to respond on LinkedIn rather than email.
Aimfox automates LinkedIn outreach campaigns: connection request with personalised note, automated follow-up message after connection acceptance, and sequence management across multiple connection stages. Per G2 reviews of Aimfox, Aimfox carries a 4.6/5 rating for LinkedIn automation reliability.
Key feature for SDRs: campaign-level analytics. Aimfox tracks connection acceptance rate, response rate, and positive response rate at the campaign level, enabling the same ICP testing methodology that is used in the email layer.
Per LinkedIn's official policy, connection request limits apply. Safe operating limits for Aimfox:
At 25 connections/day, a 30-day LinkedIn campaign produces 750 connection requests, of which 25–35% are accepted (190–260 connections), of which 15–25% generate a reply (28–65 LinkedIn replies). These LinkedIn replies are incremental to email replies from the same contacts.
| Plan | Price/month | LinkedIn accounts | Features |
|---|---|---|---|
| Solo | $47 | 1 | All features |
| Business | $97 | Up to 3 | All features + team management |
Function: Tracks every contact through the pipeline from first outreach touch to closed deal, enabling reporting on pipeline contribution by outreach channel, ICP segment, and sequence.
Why this layer is optional: The 4-layer stack (Layers 1–4) can function without a CRM; reply management via Instantly Unibox and calendar bookings cover the SDR function. CRM becomes important when: (a) the SDR hands off to an AE and handoff quality matters, (b) pipeline reporting is required, or (c) multiple SDRs are working the same territory and need to avoid duplicate outreach.
Connection to Layer 3: Most CRMs integrate with Instantly via Zapier or native integration. Per Zapier's Instantly integration documentation, triggers available include: new reply, new positive reply, contact stage change. Use the "new positive reply" trigger to automatically create a CRM record when an interested reply is detected.
| Layer | Tool | Monthly cost | Key setting | Common error |
|---|---|---|---|---|
| 1: Contact data | Quarvio | One-time purchase | ICP filter: title + size + industry | ICP filter too broad |
| 2: Infrastructure | Inframail | Flat rate | 3 inboxes/domain, warmup on | Production sends before warmup complete |
| 3: Sequencing | Instantly | $30–$77.60 | Stop-on-reply, inbox rotation | Missing suppression list |
| 4: LinkedIn | Aimfox | $47–$97 | 20–25 connections/day | LinkedIn message duplicates email angle |
| 5: CRM (optional) | Any | Varies | Positive reply trigger | Manual CRM entry instead of automation |
| Component | Monthly cost |
|---|---|
| Quarvio contact data (Growth, $199, amortised 3 months) | $66/month |
| Inframail inboxes | $100–$150/month |
| Instantly Growth | $30/month |
| Aimfox Solo | $47/month |
| Total | $243–$293/month |
At this cost level, the stack produces 300+ sends/day, 5,000+ sends/month, and at an 8% reply rate and 40% positive reply rate: approximately 160 positive replies/month, approximately 48 meetings/month (at 30% positive-reply-to-meeting conversion).
Never configure Layer 3 (Instantly) before completing Layer 1 (Quarvio). The sequence in Instantly should be written specifically for the contacts being sourced from Quarvio. If the sequence is written before the contact list is defined, it will be generic — addressing problems that may or may not match the specific ICP being contacted. Write the ICP definition first, source the Quarvio list second, write the sequence third.
The handoff between Inframail and Instantly is the point where most SDR stacks fail silently. Symptoms of failure: bounce rate above 2% (bad contacts passing through), low open rate (domain reputation low before warmup), spam complaints accumulating. Check this connection after every new inbox is added (verify the inbox in Instantly) and after every campaign launch (check Postmaster within 24–48 hours of first sends).
In Instantly Unibox, every reply should be labelled: Interested, Not Interested, Not Now, Wrong Person, or Referral. At the end of each campaign, review the Not Interested and Wrong Person labels. These replies tell you who is on the contact list but does not match the ICP. If "Wrong Person" labels are above 15% of total replies, the Quarvio ICP filter criteria need to be tightened on the next order.
The optimal timing for the Aimfox LinkedIn connection request is 2–3 days after Email 1 in Instantly. This timing creates a "pattern interrupt": the prospect sees an email from an unknown sender, then 2–3 days later receives a LinkedIn connection from the same person. This cross-channel signal increases both email open rates on subsequent sequence steps and LinkedIn connection acceptance rates, because the name is now familiar from the email.
Calculate cost per meeting monthly: (Layer 1 contact data cost + Layer 2–4 monthly costs) ÷ meetings booked. For a $250/month stack producing 25 meetings, cost per meeting is $10. As the stack scales and meeting volume increases faster than costs (because Layer 1 is a fixed purchase), cost per meeting decreases. This metric justifies stack investment to leadership and provides a benchmark for evaluating when to add additional layers (CRM, enrichment, etc.).
Symptom: All four tools are configured and active, but after 1,000+ sends, reply rate is 2–3%.
Cause: The ICP definition in Layer 1 (Quarvio filter criteria) does not match the problem being named in Layer 3 (Instantly sequence copy). A stack can be technically configured correctly but strategically misconfigured: the right tools, wrong targeting.
Fix: Before troubleshooting any individual tool, audit the ICP-sequence alignment. The Email 1 opening line should name a problem that at least 50% of the contacts on the Quarvio list experience on a regular basis. If the connection between the ICP and the problem stated in the email is not obvious, rewrite Email 1 for the specific ICP before any other diagnostic.
Symptom: Campaigns are running, sends are going out, but open rate is below 15% (indicating spam folder placement or low subject line performance).
Cause 1: Domain reputation is "Low" or "Medium" in Postmaster (spam folder placement). Cause 2: Subject line is triggering spam filters (contains promotional language, all-caps words, or excessive punctuation).
Fix: Check Postmaster for each domain first. If reputation is Low, pause production sends and continue warmup for 2–4 weeks. If reputation is High but open rate is low, the issue is the subject line. Test subject lines that are shorter (3–6 words), direct, and plain text (no emoji, no brackets, no hype words).
Symptom: Aimfox is sending 20–25 connection requests per day but only 10–15% are being accepted.
Cause: The connection request note is either too long, too commercial, or not personalised enough for the ICP.
Fix: The connection note should be under 200 characters, not commercial, and ideally reference a specific reason for connecting that is relevant to the prospect (shared industry, specific challenge, recent company announcement). The note "Exploring connections in B2B SaaS — would value the connection" is more likely to be accepted than "Hi, I wanted to connect because I have a product that helps [your role] do [generic benefit]."
Symptom: 10%+ reply rate but Unibox is 80% "Not Interested" or "Wrong Person" labels.
Cause: The contact list includes people who match the technical filter criteria (job title, company size) but are not experiencing the specific problem named in Email 1. Either the ICP is too broad or the problem statement is too generic.
Fix: Review the Not Interested and Wrong Person replies for patterns. Are they all from a specific industry? A specific company size? A specific title? Narrow the Quarvio filter criteria to exclude the sub-segments that are generating non-positive replies.
Symptom: SDR books meetings, but AE reports receiving contacts without adequate context, leading to low show rates and poor first-call quality.
Cause: The Layer 3 to Layer 5 (CRM) connection is not transferring sequence context (which emails were sent, what was said, what the prospect replied).
Fix: Configure the Zapier integration between Instantly and the CRM to pass: (1) the sequence name (which ICP segment), (2) the reply text (what the prospect actually said), (3) the labels applied in Unibox (Interested, what the interest signal was). The AE should receive this context before every meeting, not after.
Symptom: Monthly stack cost has tripled (more inboxes, higher Instantly tier, larger Quarvio packages) but meeting output has only doubled.
Cause: Cost scaling is happening across all layers simultaneously without identifying which layer was the actual constraint.
Fix: Run the constraint audit before any cost expansion. Adding Layer 2 capacity (inboxes) when the constraint is Layer 1 (ICP filter quality) scales cost without scaling meetings. The correct cost expansion sequence: first identify the constraint layer, then invest in that layer, then measure improvement, then decide whether to invest in additional capacity.
Symptom: One or two specific inboxes are showing "Bad" domain reputation in Postmaster. Campaigns using those inboxes show bounce rates of 8–15%.
Cause: Spam complaints accumulated on that domain from a previous campaign (likely due to bad contact data or too-aggressive send volume during warmup).
Fix: Immediately remove the affected domain's inboxes from all active Instantly campaigns. Check MXToolbox Blacklist Check for the domain. If listed on multiple blacklists, retire the domain and provision a replacement via Inframail. Per Mailgun's email authentication guide, check that the new domain has all three authentication records (SPF, DKIM, DMARC) configured before any sends.
Symptom: Aimfox LinkedIn replies are being handled separately from Instantly email replies. Some contacts are booking meetings via LinkedIn while the email sequence is still running to them.
Cause: The Layer 3–4 handoff (contact coordination between Instantly and Aimfox) is not bidirectional: when a prospect replies positively on LinkedIn, that contact is not being suppressed from the Instantly email sequence.
Fix: Implement a shared suppression process: when a contact replies positively in Aimfox (LinkedIn) or books a meeting, add that contact's email address to the Instantly suppression list. This prevents the email sequence from continuing to send to a prospect who has already converted via LinkedIn. A simple shared spreadsheet suppression list, checked weekly, handles this for most SDR operations.
Woodpecker's 2025 cold email benchmark study documents a direct correlation between stack completeness (all four layers configured) and reply rate. Teams with all four layers show average reply rates of 12–15%; teams with only email (Layers 1–3, no LinkedIn) show averages of 8–10%; teams with only Layer 3 (sequencing tool only, no dedicated infrastructure or verified contacts) show 3–5% average reply rates.
Instantly's 2026 benchmark report reports that the primary differentiator between average (3.43% reply rate) and elite (10%+) senders is not the tools used but the quality of configuration: ICP definition precision, contact data verification, and infrastructure warmup duration.
"The SDR stack question everyone asks is 'which tool?' The right question is 'how do these tools connect?' We had Instantly, Inframail, and Quarvio for 6 months before we figured out the correct sequence for setting them up and how the data flows between them. Once we mapped the workflow correctly, reply rate went from 4% to 11% with the same tools." — G2 reviewer, Instantly reviews on G2
| Layer | Tool | Notes |
|---|---|---|
| Contact data | Quarvio | One-time purchase, 12-month credit validity |
| Infrastructure | Inframail | Microsoft 365, automated DNS, flat rate |
| Sequencing | Instantly | Inbox rotation, Unibox, A/B testing |
| Aimfox | 4.6/5 on G2, campaign analytics |
Do I need all four layers to start outbound as an SDR?
No — start with Layers 1–3 (contact data, infrastructure, sequencing). This is the minimum viable stack that produces meetings. Add Layer 4 (LinkedIn) after the first campaign validates the ICP and produces at least 10 meetings. Adding LinkedIn before validating the ICP means running two-channel outreach against an unvalidated profile, which doubles the complexity without improving the diagnosis.
How long should warmup run before production sends?
Minimum 2–4 weeks for basic warmup. Full warmup maturity (maximum inbox deliverability capacity) takes 8–12 weeks per Woodpecker's research. In practice, most SDRs start production at 15–20 sends per inbox per day after 2 weeks, then ramp to 40 sends per inbox per day after week 6–8. Never go from zero to 40 sends/day without the warmup ramp.
Can I use my company's Google Workspace email for cold email sending?
No. Google Workspace accounts are subject to sending limits and spam policies that make cold email above 50–100/day impractical. More importantly, sending cold email from the primary company domain risks damaging the domain's reputation, which affects all company email deliverability. Always use dedicated cold email domains provisioned via Inframail.
How do I avoid contacting people in CRM opportunities?
Export active CRM contacts (leads, prospects, opportunities) as a CSV monthly. Add their email addresses to the Instantly suppression list. Cross-check every new Quarvio contact list against the suppression list before import. This prevents the cold outreach system from contacting someone who is already in an active sales conversation with a different rep.
What is the right sequence length for B2B cold email?
3–4 emails over 12–14 days. Email 1 (Day 1), Email 2 (Day 4), Email 3 (Day 8), Email 4/break-up (Day 14). Sequences longer than 4 steps rarely add positive replies and increase the risk of spam complaints from contacts who already decided not to reply to the earlier steps.
How do I know which email in the sequence is generating most meetings?
Instantly reports attribution (which sequence step the reply came from) at the campaign level. For most B2B cold email sequences, Email 1 generates 40–50% of positive replies, Email 4 (break-up) generates 20–30%, and Emails 2 and 3 generate the remainder. If Email 1 is generating under 30% of positive replies, the angle in Email 1 is weak and should be the primary optimisation focus.
How long does it take to set up the full 4-layer SDR stack?
Technical setup takes 1–2 days (domain purchase, Inframail provisioning, DNS configuration, Instantly inbox connection, Aimfox account setup). The bottleneck is warmup (2–4 weeks), not setup. Allow 3–4 weeks from starting setup to the first production campaign launch.
What metrics should an SDR report weekly?
Core weekly SDR metrics: sends (total and per inbox), open rate, reply rate, positive reply rate, meetings booked, bounce rate. Secondary metrics (monthly): cost per meeting, ICP match rate of positive replies, meetings booked by channel (email vs. LinkedIn), pipeline generated from outreach meetings.
Should I run A/B tests in my first campaign?
No. Run the first campaign without A/B testing. The goal of the first campaign is to validate the ICP and establish baseline metrics. A/B testing on an unvalidated ICP introduces two variables (ICP and copy) simultaneously, making it impossible to attribute performance differences to either. Validate the ICP first (get to 10 meetings), then A/B test copy variants.
What is the right volume for a solo SDR starting from scratch?
Start at 50–100 sends/day (3–5 warmed inboxes). This is enough volume to generate data (reply rates, bounce rates, Unibox label distribution) in 2–3 weeks without risking catastrophic infrastructure damage if the contact list or sequence has issues. Scale to 200–300 sends/day after validating ICP and confirming bounce rate is below 2%.
The stack starts with contact data.
Every send in the SDR stack traces back to a contact record. Quarvio delivers pre-verified B2B contacts filterable by job title, company size, and industry — ready to import directly to Instantly. One-time purchase, credits valid for 12 months.
