Free Tools
29 calculators for the operational decisions email infrastructure forces.
Sizing, cost, IP warming schedules, deliverability thresholds, list health, compliance — twenty-nine browser-based calculators with the data baked in. Nothing sent to a server, no signup, no email gate. Open one, enter your numbers, get the answer.
How to use these
Most calculator tools published by deliverability vendors are lead generation surfaces — three input fields, one output, and a "talk to sales" button. The tools here are different. They have more inputs, expose more knobs, and produce ranges rather than point predictions, because operational decisions in email infrastructure rarely have a single right answer. The trade-off is that you have to know what you are looking at; the calculators assume you understand what a complaint rate is before they ask you to enter one.
What the calculators are good for
Reality-checking decisions in motion. A vendor told you dedicated IPs would save 40% — the cost calculator lets you check that against your specific volume. The migration project plan says four weeks for warming; the IP warming schedule calculator says six. One of them is wrong; the calculators help you figure out which.
Translating abstractions into your numbers. "Keep complaint rate below 0.1%" is good advice that means nothing operationally. The Spam Complaint Threshold calculator translates that 0.1% into the actual number of marked-as-spam events per day at your specific volume — usually a much more useful framing.
What they are NOT good for: Replacing operational judgement. A calculator showing 87% inbox placement does not mean your campaign will hit 87%; it means the inputs you entered map to that range. The output is a starting point for an investigation, not the end of one.
Infrastructure Sizing & Capacity5 calculators
Five calculators for the architectural decisions that come before any of the day-to-day operational work. The IP pool size calculator answers the question that follows the dedicated-versus-shared decision: when does one IP become two, two become four, and how does volume per IP map to deliverability quality? The SMTP throughput calculator gives the engineering reality of how many concurrent connections, max-msg-per-connection settings, and per-IP rate limits translate to messages-per-hour at the wire. The MTA capacity planning calculator is for operators sizing the actual server hardware. The cost calculator is the one most-used in this category: it lets you adjust every variable (per-recipient ESP pricing, dedicated infrastructure cost, list size, growth rate) to compare a 12-month projection at your specific volume and pricing.
Email Infrastructure Cost Calculator
12-month ROI: dedicated infrastructure versus your current ESP. All prices adjustable to your quotes
Open calculatorIP Pool Size Calculator
When to expand from one IP to a pool, by volume tier and stream-separation needs
Open calculatorSMTP Throughput Calculator
Per-IP throughput at given concurrency, max-msg-per-connection, and per-ISP rate limits
Open calculatorMTA Capacity Planning Calculator
Server hardware sizing: cores, RAM, disk IO at projected message volume
Open calculatorEmail Volume Capacity Calculator
How much total volume your current infrastructure can sustain before scaling out
Open calculatorCost & ROI6 calculators
Six calculators for the financial framing of email infrastructure decisions. The dedicated-versus-shared IP calculator is the one to start with if you are below 100K messages per month and unsure whether dedicated makes economic sense (often it does not, despite the marketing pressure to move to dedicated). The ESP migration cost calculator estimates the full project cost — not just the new infrastructure, but the migration project itself, the warming-period revenue impact, and the operational team time. The email ROI and revenue-per-subscriber calculators move the conversation from infrastructure cost to programme contribution.
Dedicated vs Shared IP Cost Calculator
Break-even volume: when dedicated IPs become cheaper than ESP per-recipient pricing
Open calculatorESP Migration Cost Calculator
Total migration cost: new infrastructure, warming-phase revenue impact, project team time
Open calculatorEmail ROI Calculator
Revenue attributable to email versus full programme cost (sending + tooling + headcount)
Open calculatorEmail Revenue Per Subscriber Calculator
Annual revenue per subscriber benchmark, with quartiles by industry
Open calculatorEmail Infrastructure ROI Calculator
Infrastructure-specific ROI separated from programme ROI
Open calculatorSMTP Relay Cost Calculator
Cost-per-thousand at major SMTP relay providers (SES, Mailgun, SendGrid, Postmark)
Open calculatorDeliverability Health & Thresholds7 calculators
Seven calculators that quantify the operational thresholds where deliverability problems start. The complaint rate impact calculator translates a 0.1% complaint rate from an abstraction into the actual number of marked-as-spam events per day at your volume — an essential reality check, since 0.1% sounds small until it produces 5,000 daily complaints at 5M sends. The hard bounce impact and spam trap risk calculators do the same for the other two reputation signals. The Sender Score calculator, inbox placement rate calculator, and DKIM key strength checker are diagnostic tools for senders investigating an active reputation problem.
Inbox Placement Rate Calculator
Estimated inbox placement at given engagement rate, complaint rate, and authentication state
Open calculatorEmail Delivery Rate Calculator
Delivery rate (accepted at SMTP) versus inbox placement rate (post-acceptance routing)
Open calculatorSender Reputation Score Calculator
Estimated Sender Score from complaint rate, bounce rate, spam trap hits, and engagement
Open calculatorFBL Complaint Rate Calculator
0.1% complaint rate translated to actual events per day at your sending volume
Open calculatorHard Bounce Rate Impact Calculator
Reputation impact of hard bounce rate above the 2% ISP tolerance
Open calculatorSpam Complaint Threshold Calculator
Per-ISP complaint thresholds (Gmail 0.1%, Microsoft 0.3%) translated to daily event counts
Open calculatorSpam Trap Hit Risk Calculator
Probability of hitting recycled or pristine spam traps based on list source and age
Open calculatorList Health & Engagement5 calculators
Five calculators for the input side of the deliverability equation: list quality, engagement, and the operational cadence of keeping a list clean. The list hygiene savings calculator quantifies the cost of not removing inactives — the calculation usually surprises operators (a 30% inactive segment is often more than 30% of the cost). The unsubscribe rate health calculator gives the bounded ranges that distinguish a healthy programme (0.2-0.5% per send) from a programme bleeding subscribers (above 1%). The sending frequency calculator tests whether you are over- or under-mailing your specific audience.
List Hygiene Savings Calculator
Cost of mailing inactive subscribers versus removing them — usually larger than expected
Open calculatorEmail List Growth Rate Calculator
Net list growth (new subs minus unsubs and bounces) as a quality indicator
Open calculatorUnsubscribe Rate Health Calculator
Healthy unsubscribe range (0.2-0.5%) versus the warning threshold above 1%
Open calculatorEmail Sending Frequency Calculator
Optimal send frequency given engagement rate, unsubscribe rate, and list size
Open calculatorEmail Frequency vs Revenue Calculator
Diminishing returns curve: frequency where one more send produces a net negative
Open calculatorAuthentication & Compliance4 calculators
Three calculators for the regulatory and authentication layer. The SPF include limit calculator checks whether your SPF record is approaching the 10-DNS-lookup limit — the silent failure mode where SPF authentication starts failing with no obvious symptom. The DKIM key strength checker evaluates whether your DKIM keys meet the 2048-bit minimum that mailbox providers increasingly expect (1024-bit keys still work but signal an underinvestment in security). The DMARC failure impact calculator translates a failure rate from Postmaster Tools into the actual delivery impact at your domain reputation tier.
SPF Include Limit Calculator
Whether your SPF record is approaching the 10-DNS-lookup hard limit
Open calculatorDKIM Key Strength Checker
Whether your DKIM keys meet the 2048-bit minimum that modern mailbox providers expect
Open calculatorDMARC Failure Impact Calculator
Delivery impact of a given DMARC failure rate at your current domain reputation tier
Open calculatorGDPR Consent Rate Impact Calculator
Effective subscriber acquisition rate after GDPR-compliant consent collection
Open calculatorIP Warming2 calculators
Two calculators dedicated to the highest-stakes operational period in any new infrastructure: the four to six weeks of IP warming after launch. The IP warming schedule calculator generates a week-by-week sending volume schedule calibrated to destination ISP mix and starting list quality. The warm-up volume calculator answers the daily question during week one or two: "how many can I send today without overshooting the ramp?" Both calculators are built around the operational reality that warming is not just about volume — it is about engagement, complaint rate per ISP, and the order in which segments are sent.
Frequently asked questions
Where does the data behind these calculators come from?
Are the calculator outputs precise predictions, or estimates?
Do I need to enter sensitive data?
Which calculator should I use first?
Why are some calculators so simple they look like single-purpose widgets?
When the calculator answer is not actionable yet
A calculator gives you a number. The decision after the number — what infrastructure to build, when to migrate, how to architect a multi-stream programme — depends on context the calculator cannot capture. We run infrastructure assessments that turn the calculator outputs into an actual implementation plan, calibrated to your volume, list quality, and operational capacity.
Schedule an infrastructure assessment →