Updated: July 2025

At-Scale Cold Email Infrastructure: A Technical Survey

Updated: November 2025

We've spent this year reverse-engineering how cold email infrastructure actually works. Everyone claims "enterprise-grade deliverability" but few explain what that means technically. We built ColdSend after realizing most providers are selling the same underlying system with different packaging.

This isn't a ranking with fake "test results." It's a technical breakdown of architectures, a survey of Reddit sentiment, and an honest assessment of what it takes to send at 1000+ inbox scale.

The Technical Foundation

Here's what we learned: several top providers use the same enterprise infrastructure layer from a major cloud provider (think Azure, AWS, GCP). These platforms provision pre-warmed, enterprise-grade IP pools that rotate automatically. This isn't a secret — it's just that nobody advertises "we're a wrapper for [cloud provider]'s email service."

What does this mean?

• IP reputation is handled at the infrastructure level: IPs are shared across tenants but rotated intelligently. Per-customer reputation isolation is effectively real.
• "Warmup" is mostly domain reputation: Your SPF/DKIM records and sending patterns matter more than IP age.
• Setup fees are for manual provisioning: $1500 fees cover tenant creation, DNS automation, and manual QA. It's legitimate work, but it's automatable.

Hypertide charges $1500 for manual setup on this infrastructure. We automated it and bundle a sequencer. Same foundation in a different packaging.

Platform-by-Platform: What They Actually Are

ColdSend: Automated Enterprise Infra + Built-In Sequencer

Architecture: Single-tenant infrastructure using the same enterprise-grade IP pools as the major players, custom-built sequencer UI. Proper tenant isolation, dedicated IP pools per account.

Key details:

• 1000 inboxes across 10 domains (100 per domain)
• 100K emails/month included in sequencer
• No IP warmup needed (infrastructure handles this)
• Domain ramp-up still required (20-30 emails/inbox/day week 1, scaling to 100+ by week 3)
• Built-in sequencer designed for simplicity

Beta data: 10 companies, ~3000 total inboxes, 87-92% average inbox placement. Domain reputation is the variable — some users dip to 85%, others hit 94%.

Pricing: $250/month flat. No setup fees.

Our take: We built this after realizing we'd have to pay Hypertide's $1500 fee and still watch an SDR spend 3 hours/day bouncing between Instantly and spreadsheets. The infrastructure isn't novel — we just automated the provisioning and built a sequencer that doesn't require a certification course.

Hypertide: Enterprise Infra with Manual Onboarding

Architecture: Same enterprise infrastructure layer. They manually provision tenants, configure mailboxes, and hand over credentials. It's solid engineering; they just haven't automated the setup.

Key details:

• 100 inboxes per $50/month order
• 5K emails/month per order
• $1500 setup fee for manual provisioning
• Recommends "warmup" (which is really domain ramp-up)
• No sequencer — you'll pay $50-150/month for Instantly/Smartlead

Reddit sentiment: Users call the fee "painful but understandable." One agency owner: "Hypertide works but you're paying for manual provisioning. At 200+ inboxes, the math works. Below that, it's overkill."

Pricing: $50/month per 100 inboxes + $1500 setup + external sequencer costs.

Our take: If you need compliance documentation and like hand-held onboarding, Hypertide is fine. At 1000 inboxes, you're paying $500/month + $1500 + sequencer. That's 2x ColdSend's price for the same foundation plus manual setup.

Maildoso: SMTP Reseller with Shared IPs

Architecture: Bulk SMTP provider. They purchase domains, spin up mailboxes on their own SMTP infrastructure, and rotate a pool of shared IPs. No enterprise cloud backing — just reliable, old-school SMTP management.

Key details:

• SMTP credentials for any sequencer
• Shared IP pool with reputation rotation
• Automated DNS (SPF/DKIM/DMARC)
• No IP warmup needed (shared pool has reputation)
• Quarterly billing, must buy domains through them

Reddit sentiment: Mixed deliverability reports. tl;dr: "Great for first 100 inboxes, then spam rate increased to 30%." Another: "Shared IPs are the problem — one bad client ruins it for everyone."

Pricing: ~$99/quarter minimum. At 1000 inboxes, you're looking at $400/quarter + $150/month sequencer = ~$283/month.

Our take: This is the "get started cheap" option. It works until it doesn't. At 1000 inboxes, relying on shared IPs is gambling. Maildoso's reputation is solid, but shared infrastructure has natural limits.

Smartlead: Sequencer on Steroids

Architecture: Front-end for managing ESP connections. Handles warmup sequences, reply detection, and analytics. You bring your own infrastructure (Hypertide, Maildoso, Gmail, etc.).

Key details:

• $94/month base for the platform
• Warmup sequencing and monitoring
• Detailed analytics (arguably too detailed)
• API access (documentation is weak)
• No infrastructure included

Reddit sentiment: Users complain about complexity and cost. tl;dr: "Takes 3 hours to set up a simple campaign. And you still need to pay for mailboxes somewhere else."

Pricing: $94/month + infrastructure ($150-250 for 1000 inboxes) = $244-344/month.

Our take: Smartlead is feature-complete to a fault. If you have an ops team managing campaigns, it's powerful. For a lean SDR team, it's overcomplicated. The real cost is $94 plus infrastructure plus the person you need to manage it all.

Infraforge: Bare-Metal for Control Freaks

Architecture: Dedicated servers with root access. They provision bare-metal boxes, you configure Postfix/Exim, manage IPs, handle everything. This is infrastructure for engineers.

Key details:

• $2.50-4/mailbox with dedicated IP
• Full control over DNS, authentication, IP rotation
• API automation
• You manage sequencer integration

Reddit sentiment: Loved by technical agencies. tl;dr: "Amazing if you understand email infrastructure. If you don't, you'll blacklist your IPs in a week."

Pricing: ~$3000/month for 1000 dedicated IP mailboxes + sequencer.

Our take: This is what you graduate to when email is >50% of revenue. At $3000+ month, you better have a DevOps engineer. For most teams, it's unnecessary control.

Mailscale: Speed Over Substance

Architecture: Automated inbox creation with "pre-warmed" domains. They bulk-purchase aged domains, spin up inboxes instantly, and share reputation across customers.

Key details:

• 1000 inboxes in 60 seconds
• "Pre-warmed" domains (read: shared reputation)
• 95-100% deliverability guarantee (first 2 weeks only)
• Works with external sequencers

Reddit sentiment: Skeptical about longevity. "Fast but their 'pre-warmed' domains are obviously shared. Works for a month, then spam rates increase."

Pricing: $249/month for 1000 inboxes + sequencer = ~$399/month.

Our take: The guarantee is marketing — the fine print says it's void after 14 days. Speed is impressive, but sharing domain reputation is risky. Fine for testing, not for sustained campaigns.

The 1000 Inbox Reality Check

This is the benchmark where decisions get serious:

*Smartlead's infra cost is separate. Use Maildoso = $150, Hypertide = $500.

The decision matrix:

• Budget + technical skill: Infraforge (but you need engineers)
• Budget + no skill: Mailscale (but accept domain risk)
• No budget constraints: Hypertide (but pay for manual setup)
• Sane default: ColdSend (automated setup, flat pricing, included sequencer)

Why We Built This: The Setup Fee Problem

We paid Hypertide $1500. The setup took 4 days. The infrastructure worked fine — 88% inbox placement after ramp-up. But we still had to pay Instantly $150/month to actually send campaigns.

The $1500 wasn't for magic tech. It was for:

• Manual tenant provisioning
• DNS record creation
• Mailbox configuration
• QA testing

That's legitimate work, but it's automatable. We automated it and spent the Dev time building a sequencer that doesn't require a wiki to understand.

The result: Same infrastructure foundation. $1500 saved. One less subscription.

Technical Recommendations for 1000 Inboxes

Startups (Testing PMF)

Use Mailscale ($249): Accept the domain risk while you validate. If it works, migrate to ColdSend or Hypertide for serious volume.

Growing Agencies (100-500 inboxes)

Use ColdSend ($250): Solid infra, flat pricing, simple sequencer. Focus on messaging, not tooling.

Enterprise Agencies (1000+ inboxes)

Evaluate Hypertide ($500): If you need compliance docs and have clients asking for manual provisioning proof, pay the fee. Otherwise ColdSend's automation is fine.

Technical Teams (1000+ inboxes)

Use Infraforge ($3000): If you have DevOps resources, the control is worth it. For everyone else, it's overkill.

The Warmup vs. Ramp-Up Clarification

Traditional Warmup (Maildoso, Smartlead, etc.):

• Week 1: 5-10 emails/inbox/day
• Weeks 2-4: Gradually increase to 30-50/day
• You're idle, burning cash

Conservative Ramp-Up (ColdSend, Hypertide if honest):

• Day 1: 20-30 emails/inbox/day
• Week 2: 40-50/day
• You're generating leads while building domain rep

The difference isn't technical — it's honesty about what "warmup" actually means.

Bottom Line: What You're Actually Pay For

At 1000 inboxes, you're not buying technology — you're buying packaging:

• Hypertide: Manual setup + enterprise hand-holding
• Maildoso: Shared SMTP with automated DNS
• Smartlead: Complex sequencer that needs external infra
• Infraforge: Bare-metal control for engineers
• Mailscale: Speed and shared domain risk
• ColdSend: Automated enterprise infra + simple sequencer

Same foundation? Mostly. Same experience? No.

We built ColdSend because we were tired of explaining to our SDR why he needed 4 dashboards to send an email.