Comparison
Feb 14, 2026
CEO and co-founder
How to Choose Cold Email Infrastructure: Buyer's Guide & Evaluation Criteria
Updated January 22, 2026
TL;DR: The right cold email infrastructure decision comes down to 10 weighted criteria: deliverability validation, true cost per inbox at scale, setup time, contract flexibility, support quality, compliance features, IP type, scalability, integrations, and security. For agencies managing 50-200 domains, Google Workspace costs $350-420/month for 50 inboxes. Flat-rate providers like Inframail charge $129/month for unlimited inboxes. Use the decision matrix in this guide to score vendors objectively and watch for red flags like hidden quarterly billing, shared IP contamination, and missing blacklist monitoring.
Bad infrastructure decisions drain agency budgets through sunk domain costs, wasted setup time, and client churn when deliverability tanks. I've watched agencies lose entire campaigns because their shared IP pool got flagged by another user's spam behavior. I've seen founders trapped by quarterly contracts they signed before validating deliverability claims.
This guide gives you the evaluation framework to avoid those mistakes. You'll walk away with specific metrics to demand, questions to ask, red flags to spot, and a weighted scoring matrix you can use to compare any vendor objectively.
Why infrastructure choice matters more than your email copy
Your infrastructure determines whether prospects ever see your carefully crafted message. According to Validity's 2024 Email Deliverability Benchmark, ESPs block or spam-filter roughly one in six emails, with the global inbox placement average hovering around 84%. Gmail leads at 87.2%, while Outlook trails at 75.6%.
The cost math most founders ignore
Google Workspace Business Starter pricing creates painful margin squeeze fast. At $7-8.40 per inbox per month, the math compounds:
Inbox Count | Google Workspace Cost | Inframail Cost | Monthly Savings |
|---|---|---|---|
50 inboxes | $350-420/month | $129/month + ~$68.50 domains | $152.50-222.50/month |
100 inboxes | $700-840/month | $129/month + ~$137 domains | $434-574/month |
200 inboxes | $1,400-1,680/month | $129/month + ~$274 domains | $997-1,277/month |
For agencies operating on 15-20% net margins, infrastructure consuming 2.5-3.0% of client billings creates an unsustainable cost structure. Watch our breakdown of dedicated IP vs shared IP pools for cold email to understand why IP type impacts both deliverability and cost.
The time drain nobody budgets for
Setting up 50 cold email domains manually takes 12+ hours. You're logging into DNS panels, creating SPF records (v=spf1 include:spf.protection.outlook.com ~all), configuring DKIM, setting DMARC policies, waiting 24-48 hours for propagation, then testing with Mail-Tester before campaigns can launch.
"Inframail makes it remarkably easy to purchase domains, configure them correctly, create inboxes, and initiate warm-up immediately. The level of automation is exceptional and clearly designed for serious operators." - Verified user review of Inframail
That 12+ hours needs to go toward sales calls, client strategy, and campaign optimization. Infrastructure setup must take minutes, not days.
The 10 evaluation criteria that actually matter
I've ranked these criteria by weight based on how agency founders actually make buying decisions. SaaS buyers now split 42% monthly and 45% annual on subscription preferences, reflecting the balance between flexibility and cost savings.
1. Deliverability validation Inframail has 38 5-star reviews on Trustpilot. (weight: 30%)
This criterion matters most, yet it's the hardest to verify before purchase.
What to demand:
Inbox placement rate data: The global average sits around 84% according to Validity. Top performers exceed 90%. Anything below 80% signals problems.
Testing methodology disclosure: Demand sample size details, test parameters, and which ESPs they tested against.
Third-party verification: Require Mail-Tester scores of 9+/10, GMass inbox rate testing results, or similar independent validation.
Red flag: Claims of "lookalike or better deliverability vs Google and Outlook" without published test data. Industry forums and agency communities consistently report deliverability gaps of 10-15% below Google/Outlook when vendors don't publish independent test results.
Inframail reports 9.5/10 on Mail-Tester and 88% inbox rate via GMass testing. These numbers should serve as your baseline expectation from any vendor.
2. True cost per inbox at scale (weight: 25%)
The pricing page number never tells the full story. You need Total Cost of Ownership (TCO) across four components:
Platform fee: Monthly subscription
Domain costs: $16.44 per domain per year
Warmup tools: $15-50/month per inbox if not included
Sending platform: Instantly, Smartlead, or similar (pricing varies by tier)
TCO calculation example for 50 inboxes:
Cost Component | Google Workspace | Flat-Rate Provider |
|---|---|---|
Platform/inboxes | $350-420/month | $129/month |
Domains (amortized) | ~$68.50/month | ~$68.50/month |
Warmup (external) | N/A | $50-100/month |
Total | $418.50-488.50/month | $247.50-297.50/month |
The flat-rate model wins at scale because infrastructure costs don't grow linearly with inbox count. Learn how to send 1,000+ cold emails per day without exploding your infrastructure budget.
3. Setup time and DNS automation (weight: 20%)
Speed of deployment matters when campaigns need to launch fast. Benchmark what vendors claim against these standards:
Automated DNS configuration: The platform must configure SPF, DKIM, DMARC records automatically without manual panel access
Inbox provisioning time: Expect under 5 minutes for 10 inboxes with full automation
Credential export: One-click CSV export to Instantly, Smartlead, or your sending platform
"I personally have over 1,000 email accounts with Inframail for one flat price. Adding all those records would have probably taken dozens of hours. Instead all records were added within 10 minutes." - Verified user review of Inframail
Critical warmup timeline: Even with instant setup, you need 2-4 weeks of warmup before sending cold emails. ESPs treat domains younger than a month as suspicious. Read our guide on how to warm up email domains for cold email campaigns.
4. Contract flexibility (weight: 10%)
Your contract preference should match your validation needs:
Monthly billing:
Allows 30-45 day pilots before commitment
Higher headline rate (typically 15-20% premium over annual)
Best for testing deliverability claims with real campaigns
Annual billing:
Lower effective monthly cost
Often unlocks additional features
Only commit after successful pilot
Red flag: Forced quarterly billing or 12-month contracts before you can validate performance with real campaigns. Always check whether month-to-month options exist before signing.
5. Support quality (weight: 10%)
We've found that higher-tier annual contracts usually include augmented support channels. Here's what to look for:
Response time SLA: Clear commitments by issue severity (critical issues should get faster response than routine questions)
Channel availability: Email, chat, and ideally Slack or phone for urgent deliverability problems
Technical expertise: Access to deliverability specialists, not just tier-1 support
Documentation quality: Help centers that explain capacity planning and troubleshooting
"One of the best mailbox infra vendors I have ever used super easy and quick setup and support is practically 24/7 with at max a 2min wait to get a question answered." - Verified user review of Inframail
Inframail provides 16 hours of daily support from real people, plus one-on-one deliverability consulting on higher tiers.
6. Compliance features (weight: 8%)
Cold email operates in a legal gray zone that creates real churn risk if you get compliance wrong. Your infrastructure needs specific capabilities to stay compliant.
CAN-SPAM requirements (US):
Clear sender identification
Honest subject lines
Functional unsubscribe link in every message
Valid physical postal address
Honor opt-out requests within 10 business days
GDPR requirements (EU contacts):
Legitimate interest documentation for B2B outreach
Data minimization (only collect names, emails, job titles, company info)
Clear disclosure of data processing
Unsubscribe mechanism in every email
Right to erasure compliance
According to Recital 47 of GDPR, cold emails are legal as long as you have legitimate interest to contact prospects. Your infrastructure should support compliance through proper authentication and easy unsubscribe handling.
7. IP infrastructure: dedicated vs shared (weight: 7%)
This architectural decision affects your reputation control and risk exposure.
Dedicated IPs:
Your sending behavior alone determines reputation
No contamination from other users' spam
Higher cost but predictable deliverability
Best for agencies managing multiple clients
Shared IPs:
Lower cost per inbox
Rely on IP rotation to spread risk
One bad actor can damage the entire pool
You inherit reputation risk from every other user on the pool
Inframail provides 1 dedicated US-based IP on the Unlimited Plan ($129/month) and 3 dedicated IPs on the Agency Pack ($327/month, or approximately $199/month with annual billing). Watch our video on dedicated IP vs shared IP pools for deeper analysis.
8. Scalability (weight: 5%)
Your infrastructure must scale with your client portfolio without creating operational chaos.
Key scalability factors:
Daily domain/inbox limits: Can you set up 20-50 domains in a single day when onboarding a new client?
Warmup pipeline: Do you have additional mailboxes warming in the background to replace anything that gets burned?
Cost trajectory: Does your infrastructure bill double when clients double, or stay flat?
Safe benchmarks for scaling: 20-40 domains with 2-3 inboxes each. Keep total volume across all inboxes under 200 emails per domain daily to maintain reputation.
9. Integration capabilities (weight: 3%)
Your infrastructure needs to connect cleanly to sending platforms, warmup tools, and potentially CRMs without requiring custom development.
Essential integrations:
CSV export with IMAP/SMTP credentials
Compatibility with Instantly, Smartlead, Lemlist, or your preferred sender
API access for custom workflows
"Product works great, it's super easy to buy domains/inboxes, very easy to pair with smartlead (or another sender)." - Verified user review of Inframail
Check out the InfraMail setup tutorial for cold email to see the integration workflow in practice.
10. Security and data protection (weight: 2%)
For enterprise clients or regulated industries, security certifications matter.
Certifications to ask about:
SOC 2: Focuses on data security, availability, and processing integrity
ISO 27001: Information security management system standard, most commonly requested by European clients
Data security questions:
Where is data stored geographically?
What encryption standards apply (in transit and at rest)?
What are breach notification protocols?
How often do third-party security audits occur?
Inframail is built on Microsoft's cloud platform, providing infrastructure credibility for security-conscious buyers.
Red flags that should kill any deal
These warning signs indicate vendors who cost you more in the long run, regardless of headline pricing.
Deliverability red flags
No published test data: If they can't show Mail-Tester scores or inbox placement rates with methodology, assume the worst
"Best-in-class deliverability" claims without proof: Marketing language without numbers signals they're hiding something
Mixed reviews across platforms: Glowing testimonials on their site but complaints about spam rates on Reddit means the truth lies somewhere between
No blacklist monitoring: If you won't know when your domain or IP gets flagged, you'll learn via angry client calls
Pricing red flags
Hidden quarterly billing: Discovering you're locked into 3-month minimums at checkout destroys budget planning
"Book a demo" to see pricing: Forcing enterprise sales processes for $129/month tools wastes everyone's time
Warmup "included" without actual functionality: Some vendors market warmup as included but the feature requires external tools to function properly
Guarantees void after 14 days: Fine print that nullifies money-back promises before you can validate performance
Infrastructure red flags
Shared IPs without rotation: Always relying on the same IPs for every send, no rotation to distribute risk
"Pre-warmed" domains shared across users: Domain reputation works for the first month, then spam rates increase as you realize dozens of other senders are using the same domains
No dedicated IP option: If dedicated IPs aren't available at any price point, you have no path to reputation isolation
US-only infrastructure for global sending: Data residency requirements matter for EU and APAC markets
Support and transparency red flags
No response time commitments: Vague "we'll get back to you" language gives you no accountability when deliverability crashes Friday afternoon
Limited documentation: If the help center can't answer basic setup questions, expect problems
Founder inaccessible: Early-stage infrastructure companies should have founders reachable via LinkedIn or support channels
Questions to ask every vendor before signing
Copy this list. Use it on every demo call and in every vendor evaluation.
Deliverability questions
What is your average inbox placement rate across all customers? Can you provide recent test results with methodology?
How do you handle domain warmup? What timeline do you recommend before sending cold emails?
Which authentication protocols (SPF, DKIM, DMARC) do you configure automatically?
Do you offer inbox placement testing tools, or do I need third-party services?
What happens when a domain or IP gets blacklisted? Do you have automated delisting?
Pricing questions
What is the total cost per inbox including all fees (setup, domains, warmup)?
Are there volume discounts? At what thresholds do they apply?
What are the costs for additional services (dedicated IPs, SSL, domain masking)?
Is there a price lock for annual contracts? What happens at renewal?
What's your refund policy if deliverability doesn't meet expectations?
Infrastructure questions
Do you offer dedicated or shared IPs? What are the trade-offs of each?
How many domains and inboxes can I set up daily?
What is your approach to IP rotation?
Can I bring my own domains, or must I purchase through you?
Where are your servers located? Do you offer non-US infrastructure?
Support questions
What are your support response time SLAs by issue severity?
Do you offer dedicated account management for larger accounts?
What channels are available (email, chat, phone, Slack)?
Is technical deliverability expertise available beyond tier-1 support?
Can you provide 3-5 referenceable customers at my scale willing to take calls?
Contract questions
What are the contract terms (monthly, annual, multi-year)?
What is the cancellation notice period?
How do I export my data if I decide to leave?
Are there any auto-renewal clauses I should know about?
Can I pilot 10-20 domains for 30 days before committing to full infrastructure?
Decision matrix: How to score and compare vendors
Use this framework to compare any vendors objectively. Download a spreadsheet, plug in your scores, and let the math make the decision.
Matrix structure
Create rows for each criterion and columns for each vendor:
Criterion | Weight | Vendor A | Vendor B | Vendor C |
|---|---|---|---|---|
Deliverability | 3x | Score 1-5 | Score 1-5 | Score 1-5 |
Cost at scale | 2.5x | Score 1-5 | Score 1-5 | Score 1-5 |
Setup time | 2x | Score 1-5 | Score 1-5 | Score 1-5 |
Contract flexibility | 1x | Score 1-5 | Score 1-5 | Score 1-5 |
Support quality | 1x | Score 1-5 | Score 1-5 | Score 1-5 |
Compliance | 0.8x | Score 1-5 | Score 1-5 | Score 1-5 |
IP infrastructure | 0.7x | Score 1-5 | Score 1-5 | Score 1-5 |
Scalability | 0.5x | Score 1-5 | Score 1-5 | Score 1-5 |
Integrations | 0.3x | Score 1-5 | Score 1-5 | Score 1-5 |
Security | 0.2x | Score 1-5 | Score 1-5 | Score 1-5 |
Weighted score = (Score × Weight) summed across all criteria
Scoring guidelines
For deliverability:
5 = >90% inbox placement with published proof
4 = 85-90% with mixed but positive reviews
3 = 80-85% or limited data available
2 = <80% or concerning reviews
1 = No data or poor reputation
For cost:
5 = Lowest TCO at your scale (50/100/200 inboxes)
4 = Within 20% of lowest TCO
3 = Within 40% of lowest TCO
2 = 40-60% higher than lowest
1 = >60% higher than lowest
For setup time:
5 = <5 minutes for 10 inboxes with full automation
4 = 5-15 minutes with partial automation
3 = 15-30 minutes with some manual steps
2 = 30-60 minutes requiring DNS panel access
1 = >60 minutes or fully manual
Deal-breakers (automatic disqualification)
These criteria override the scoring matrix. If a vendor fails any of these, remove them from consideration:
No month-to-month option when you need to test
Shared IPs without rotation for high-volume needs
No blacklist monitoring
Bounce rate above 2% in testing
Missing required compliance certifications for your clients
No data export option
Matching infrastructure to your needs
Not every agency needs the same solution. Match your infrastructure choice to your specific situation.
By company size
Solo founders and small teams (1-5 people):
Protect runway by choosing monthly plans
Accept slightly higher rates for flexibility
Start with 20-30 domains to validate
Focus on setup automation to save time
Mid-sized agencies (5-15 people):
Consider annual contracts after successful 30-day pilot
Budget $200-400/month for infrastructure
Prioritize dedicated IPs for client isolation
Need scalability to 100-200 domains
Larger operations (15+ people):
Negotiate custom pricing for 500+ inboxes
Require dedicated account management
Security certifications matter for enterprise clients
Consider multiple infrastructure providers for redundancy
By sending volume
Daily Volume Target | Infrastructure Need |
|---|---|
500 emails/day | 15-20 inboxes across 5-10 domains |
1,000 emails/day | 30-40 inboxes across 10-15 domains |
2,500 emails/day | 75-100 inboxes across 25-40 domains |
5,000 emails/day | 150-200 inboxes across 50-80 domains |
The math: Each inbox should send 30-50 emails per day maximum. Attach 2-5 mailboxes per domain. Keep total volume per domain under 200 emails daily to maintain reputation.
By use case
Lead generation agencies: Need dedicated IPs, scalability, and integration with Instantly or Smartlead. Cost predictability matters because you bill clients fixed retainers.
In-house SDR teams: Can tolerate slightly lower flexibility for better pricing. Integration with CRM (Salesforce, HubSpot) matters more.
Recruiting firms: Similar needs to lead gen but often smaller volume. May prioritize deliverability over cost.
Watch how cold email strategy works for B2B SaaS to understand use-case specific requirements.
How to run a proper trial
Don't commit full infrastructure budget before validating performance with real campaigns.
Testing methodology
Week 1-2: Setup and warmup
Purchase 10-20 domains through the platform
Create 2-3 inboxes per domain
Begin warmup process (Day 1-2: 5 emails sent/received per day)
Monitor for any immediate deliverability issues
Week 3-4: Gradual ramp
Increase warmup to 20-30 emails/day by Day 10
Run Mail-Tester checks on 5-10 inboxes
Begin small cold campaigns (50-100 emails/day total)
Track inbox placement across Gmail, Outlook, Yahoo
Week 5-6: Full validation
Scale to 200-500 emails/day
Measure inbox placement rate (target: >85%)
Track bounce rate (target: <2%)
Monitor spam complaints (target: <0.1%)
Evaluate support responsiveness through real tickets
Success criteria
Your trial passes if you achieve:
Inbox placement: >85% across major ESPs
Bounce rate: <2%
Spam complaints: <0.1%
Setup time: Actual time stays within 20% of vendor claims
Support response: Every ticket answered under stated SLA
If the trial fails on any metric, document the gap and either negotiate improvements or move to your next vendor option.
Ready to cut your infrastructure costs by $1,830-2,670 annually?
The evaluation framework in this guide works for any cold email infrastructure provider. Start by calculating your true TCO across 50, 100, and 200 inboxes. Run the vendor questions past every provider on your shortlist. Use the decision matrix to score objectively.
For agencies running 50-200 domains who need predictable costs and automated DNS setup, Inframail offers flat-rate unlimited inboxes at $129/month with dedicated US-based IPs. You'll reclaim 10-12 hours monthly currently spent on DNS configuration and redirect that time to sales calls that actually grow revenue.
"The infrastructure I've purchased has been working great for our company for the past 6 months and has been a lot better value than setting up elsewhere. The support team are quick to help with any issues or quieries." - Verified user review of Inframail
Sign up to Inframail and get started today.
FAQs
How many inboxes do I need for 1,000 emails per day?
You need 30-40 inboxes spread across 10-15 domains. Each inbox should send no more than 30-50 emails per day to maintain deliverability.
What's a good inbox placement rate for cold email?
The global average is around 84%. Target 85%+ for reliable campaign performance.
How long does domain warmup take?
Plan for 2-4 weeks of warmup before sending cold emails. ESPs treat domains younger than one month as suspicious.
Should I choose dedicated or shared IPs?
Dedicated IPs give you reputation isolation. Your behavior alone determines deliverability.
What's the true cost difference between Google Workspace and flat-rate providers?
For 50 inboxes: Google Workspace costs $350-420/month. Inframail costs $129/month plus ~$68.50/month in domains.
Can I bring my own domains or must I purchase through the platform?
Most infrastructure providers support both domain purchase and migration. Check provider documentation for transfer timelines.
Key terms glossary
Dedicated IP: An IP address used exclusively by your organization for sending emails. Your reputation isn't affected by other senders.
Shared IP pool: Multiple senders share the same IP addresses. IP rotation distributes sends across the pool to spread reputation risk.
SPF (Sender Policy Framework): A DNS record specifying which mail servers can send email for your domain. Prevents spammers from forging your domain as sender.
DKIM (DomainKeys Identified Mail): An authentication method adding a digital signature to emails, verifying they haven't been altered in transit.
DMARC (Domain-based Message Authentication): A protocol telling receiving servers how to handle emails that fail SPF or DKIM checks.
Inbox placement rate: The percentage of sent emails landing in the primary inbox rather than spam, promotions, or being blocked entirely.
Domain warmup: The process of gradually increasing sending volume from a new domain to build sender reputation with ESPs.
TCO (Total Cost of Ownership): The complete cost of infrastructure including platform fees, domains, warmup tools, and sending platform.
