How Smartlead + ColdRelay Work Together
ColdRelay (Infrastructure)
ColdRelay provides the mailboxes Smartlead sends from. Each mailbox is a Microsoft 365 account on a dedicated, isolated Azure tenant with its own dedicated IP, fully-automated DNS (SPF, DKIM, DMARC), and a 95% inbox-placement guarantee. ColdRelay's pricing is per-mailbox: $1 (1-199), $0.85 (200-999), $0.70 (1K-4,999), $0.55 (5K+). Setup completes in 60 minutes, no warmup wait.
Smartlead (Sending Platform)
Smartlead is a cold email orchestration platform — it handles multi-step sequences, a unified master inbox, AI-powered reply detection, spintax, and conditional sequence logic across hundreds or thousands of mailboxes. Smartlead does NOT provide the underlying email infrastructure. You bring your own mailboxes via SMTP/IMAP credentials, and Smartlead routes sends across them.
Why use them together
Smartlead is the brain (sequences, master inbox, reply AI, analytics). ColdRelay is the body (mailboxes, IPs, DNS). The combination gives you a clean separation: Smartlead handles campaign logic, ColdRelay handles infrastructure quality. Because the two are loosely coupled over standard SMTP/IMAP, swapping either side later is straightforward — the ColdRelay mailboxes work with any sending platform.
Connect Smartlead to ColdRelay (Step-by-Step)
- 1
Order ColdRelay mailboxes
Sign up at coldrelay.com/sign-up, pick a domain (ColdRelay handles registration for $14), and order your mailbox count. The minimum is 50 mailboxes ($50/month at the base tier). ColdRelay's automation provisions the dedicated mail server, registers the domain, and creates all mailboxes inside an isolated Azure tenant.
Note: Provisioning takes 60 minutes end-to-end. You'll receive a CSV with every mailbox's SMTP host, port, username, and password once it's complete.
- 2
Wait for DNS propagation
ColdRelay configures SPF, DKIM, and DMARC records automatically on the new domain. DNS propagation usually completes in under an hour but can take up to 24. You can verify with the Email Deliverability Test at coldrelay.com/tools/email-deliverability-test — when SPF, DKIM, DMARC, and MX all show as configured, you're ready.
Note: Don't start sending before all four records (SPF, DKIM, DMARC, MX) verify correctly. Sending before authentication is in place causes immediate spam-folder placement.
- 3
Connect mailboxes to Smartlead
In Smartlead, go to Email Accounts → Add Email Account → Custom SMTP/IMAP. For each ColdRelay mailbox, paste its SMTP host (box.YOURDOMAIN.com), SMTP port (587), SMTP username (the full email address), and the password from the ColdRelay CSV. Repeat the IMAP section using port 993 with TLS. Smartlead validates the connection and marks the mailbox as Active once both sides authenticate.
Note: Smartlead supports bulk CSV import for email accounts under Email Accounts → Bulk Upload. The ColdRelay CSV maps directly to Smartlead's expected column layout, so 200+ mailboxes can be onboarded in a single upload instead of one-by-one.
- 4
Set daily limits per mailbox
In each Smartlead mailbox's settings, set the daily send limit to 2 outbound emails per day. This matches ColdRelay's per-mailbox cap (designed for optimal deliverability, not maximum volume). With 50 mailboxes you can send 100 outbound emails/day; 200 mailboxes = 400/day; 1,000 mailboxes = 2,000/day. Also set a minimum wait time between sends (5-10 minutes) under the campaign-level throttling settings.
Note: Going higher than 2/day/mailbox is the single fastest way to degrade deliverability. ColdRelay's pricing model assumes 2/day — if you need 5,000+ emails/day, add more mailboxes, don't push existing ones harder.
- 5
Enable Smartlead's warmup
Turn on Smartlead's built-in warmup for each mailbox via the Warmup toggle in the email account settings. Set the daily warmup volume to 2 emails, ramp-up of 1/day, and reply rate around 40%. Smartlead's warmup runs on a peer-warming network — your mailboxes exchange emails with other Smartlead warmup-network mailboxes, which builds engagement signals at Gmail and Outlook.
Note: ColdRelay mailboxes ship reputation-ready (the Azure tenant + dedicated IP isolation gives you a clean start) but warmup is still recommended for the first 2 weeks of active sending. Smartlead's warmup runs in parallel with active campaigns, so keep both totals within the 4/day/mailbox ceiling.
- 6
Configure your first campaign
In Smartlead, create a campaign, upload your prospect list (CSV with email + custom variables), build your sequence with subject lines + email bodies + follow-up timing, and assign your ColdRelay mailboxes as sending accounts. Smartlead distributes sends across all assigned mailboxes respecting each one's daily cap. Use Smartlead's spintax syntax {opt1|opt2|opt3} on subject lines and opening sentences to vary fingerprints.
Note: Smartlead supports conditional sequence logic — different follow-up paths based on opens, clicks, or replies. The Spintax Generator at coldrelay.com/tools/spintax-generator produces the syntax Smartlead expects.
- 7
Set up the master inbox and reply handling
Smartlead aggregates replies from every connected mailbox into the Master Inbox. Verify each ColdRelay mailbox shows under Master Inbox → Connected Accounts. Smartlead's reply-detection AI auto-categorizes replies (interested, not interested, out-of-office, unsubscribe) and pauses sequences automatically when a prospect responds. No extra configuration is needed on the ColdRelay side — IMAP polling on port 993 handles it.
Note: If replies aren't appearing in the master inbox, the IMAP credentials likely didn't validate at connect time. Re-test from the email account's Connection Status page.
- 8
Monitor deliverability ongoing
Run the Email Deliverability Test weekly to verify SPF/DKIM/DMARC stay passing. Smartlead's Analytics dashboard shows open and reply rates per mailbox — flag any mailbox with reply rates below your campaign average. Check Google Postmaster Tools for spam-folder rates and IP reputation. ColdRelay automatically monitors blocklists — you'll get an alert if any of your dedicated IPs hit a major blocklist (Spamhaus, Barracuda, SORBS, SpamCop).
Note: ColdRelay's 95% inbox-placement guarantee is contingent on following the 2/day/mailbox cap. Exceeding the cap voids the guarantee.
Key Considerations for Smartlead + ColdRelay
Daily send limits per mailbox
Set Smartlead's per-mailbox daily limit to 2 outbound + 2 warmup = 4 total/day MAX. This is ColdRelay's optimal-deliverability cap. Going higher is the single biggest cause of mailbox burnout we see. Scale total volume by adding more mailboxes, not by pushing existing ones harder.
Dedicated IPs end shared-IP risk
Each ColdRelay mailbox is on a dedicated IP within your isolated Azure tenant. Other Smartlead users sending from shared infrastructure share IP reputation with random other senders — bad actors on the same IP damage everyone's deliverability. With ColdRelay your IP reputation is entirely your own.
Smartlead's master inbox works as expected
Smartlead's master inbox aggregates replies across all your mailboxes via IMAP polling on port 993. ColdRelay's IMAP setup is standard — no special configuration needed. Smartlead's reply-detection AI categorizes responses and pauses sequences automatically when prospects engage.
Switching cost is low
If you decide Smartlead isn't right and want to switch to Instantly, EmailBison, or another sender later, your ColdRelay mailboxes work with any platform that supports custom SMTP/IMAP. You don't lose the infrastructure investment — just reconnect each mailbox at the new platform.
Domain-rotation strategy
ColdRelay caps each domain at 100-150 mailboxes for deliverability reasons. If you need 500+ mailboxes, you'll order multiple domains. Smartlead handles multi-domain campaigns natively — assign mailboxes from each domain to different campaign tracks, or let Smartlead round-robin across all domains within one campaign to spread risk.
Smartlead's unlimited-mailbox pricing
Smartlead doesn't charge per mailbox — the Basic plan ($39/month) supports unlimited connected accounts. This means your ColdRelay mailbox count scales independently of Smartlead's cost, unlike sender-platform pricing tied to mailbox or send volume. For large operations (500+ mailboxes), this is a meaningful structural advantage.
Pricing Snapshot
ColdRelay
ColdRelay's per-mailbox cost ranges from $1.00 (1-199 mailboxes) down to $0.55 (5,000+). Domain registration is $14/year, one-time. For 200 mailboxes: 200 × $0.85 = $170/month + $14 annual domain cost.
Smartlead
Smartlead's pricing is plan-based, not mailbox-count-based. Basic plan ($39/month) gives unlimited connected mailboxes, unlimited warmup, and no per-mailbox daily-send cap. Pro plan ($94/month) adds API access, custom domain tracking, webhooks, and team seats. Custom (enterprise, starts ~$174/month) adds higher contact and active-lead allowances plus dedicated support. Pricing scales by leads and features, not by mailbox count.
Total monthly
A typical 200-mailbox cold email operation: ColdRelay infrastructure at ~$170/month + Smartlead Pro at $94/month = ~$264/month total. At 1,000 mailboxes: ColdRelay $700/month + Smartlead Pro $94/month = ~$794/month. Smartlead's flat-fee structure makes the combined cost especially attractive at high mailbox counts — compare against Google Workspace at $6+/mailbox/month, where 200 GW mailboxes alone would be $1,200/month before Smartlead's sender cost.
Common Issues + Fixes
⚠ Mailbox shows 'Connection Failed' or 'Authentication Error' in Smartlead
Re-check the SMTP/IMAP credentials against the ColdRelay CSV — the most common cause is a typo in the host (it's box.YOURDOMAIN.com, not mail.YOURDOMAIN.com) or wrong port (SMTP 587, IMAP 993, both with TLS). If credentials look correct, hit Test Connection on the email account page in Smartlead. If still failing, regenerate the mailbox password from the ColdRelay dashboard and reconnect.
⚠ Warmup enabled in Smartlead but engagement rates not climbing
Smartlead's warmup network needs 7-14 days to ramp up engagement signals. Verify the daily warmup volume is set to 2 emails (not 0), the reply rate is around 40%, and the mailbox shows Warmup Active under its settings page. If a mailbox has been warming for over two weeks with no improvement, check the Email Deliverability Test results for the domain — failing SPF/DKIM/DMARC will block warmup engagement signals.
⚠ Emails landing in spam at Gmail
Run the Email Deliverability Test against the domain. If SPF, DKIM, or DMARC fails, the records may not have propagated yet — wait 24 hours. If all pass, check Google Postmaster Tools for the domain's spam-folder rate. The most common cause of post-authentication spam placement is exceeding the 2/day/mailbox cap in Smartlead, followed by campaign content (spammy subject lines, link density too high, no plain-text alternative).
⚠ Inbox-placement test (Mail-Tester, GlockApps) shows missing DKIM
ColdRelay's DKIM is on the domain's _dkim.YOURDOMAIN.com selector. If a test reports missing DKIM, it usually means the test ran before DNS propagation completed. Wait 24 hours from provisioning and re-test. If still missing, contact ColdRelay support — there's a deliverability consultant included at higher mailbox volumes.
⚠ Master inbox shows no replies even though prospects are replying
Smartlead polls IMAP on port 993 with TLS to surface replies. Verify the IMAP credentials match the ColdRelay CSV — most commonly the IMAP password is the same as SMTP but can drift if a mailbox was reset. Re-test in Smartlead's email account settings (Test Connection button). Also confirm the mailbox is included under Master Inbox → Connected Accounts; some accounts get excluded if their initial IMAP validation fails.
Frequently Asked Questions
Do I need ColdRelay if I already have Smartlead?
Smartlead is a sending platform — it doesn't provide mailboxes or DNS. You need an infrastructure provider (ColdRelay, Google Workspace, etc.) underneath it. Most Smartlead users start with Google Workspace mailboxes ($6+/mailbox/month) and switch to ColdRelay because the infrastructure is purpose-built for cold email at a fraction of the cost ($0.55-$1.00/mailbox).
Is ColdRelay better than Google Workspace for use with Smartlead?
For cold email at any scale beyond a handful of mailboxes: yes. Google Workspace charges $6+/mailbox/month and shares some risk across all GW senders. ColdRelay charges $0.55-$1.00/mailbox/month, gives each customer a dedicated Azure tenant with dedicated IPs, and bakes SPF/DKIM/DMARC automation into provisioning. The infrastructure quality is closer to enterprise-grade at indie-tool prices.
How many mailboxes do I need to scale to my target send volume?
ColdRelay's per-mailbox cap is 2 outbound emails/day for optimal deliverability. So if you want to send 1,000 emails/day, you need 500 mailboxes. The Mailbox Calculator at coldrelay.com/tools/mailbox-calculator lets you input your target volume and gives you the exact mailbox count + pricing tier.
Can I use ColdRelay with Smartlead's Basic plan?
Yes. Smartlead Basic ($39/month) supports unlimited connected mailboxes and unlimited warmup, which pairs especially well with ColdRelay's per-mailbox pricing — your sender-platform cost stays flat as your mailbox count grows. You'll only need to upgrade to Pro if you want API access (for automating ColdRelay → Smartlead mailbox sync) or webhook integrations.
Will my Smartlead campaigns break if I switch to ColdRelay from another provider?
No. Switching infrastructure providers mid-campaign requires reconnecting each mailbox in Smartlead (new SMTP/IMAP credentials), but campaign logic, sequences, spintax, master-inbox history, and contact lists stay intact. The transition takes a few minutes per mailbox — faster with Smartlead's bulk CSV upload. We recommend pausing campaigns during the swap to avoid any deliverability blips.
Does Smartlead's warmup network conflict with ColdRelay's deliverability setup?
No. Smartlead's warmup runs over standard SMTP/IMAP just like outbound sends, so it works transparently on ColdRelay mailboxes. Keep the combined daily total within the 4/day ceiling (2 outbound + 2 warmup). ColdRelay mailboxes ship reputation-ready, but warmup still helps build engagement signals at Gmail and Outlook during the first 2 weeks.
What if Smartlead's deliverability is bad with my ColdRelay mailboxes?
That's almost always a campaign-content issue (subject lines triggering spam filters, link density too high, sender names looking off) rather than an infrastructure issue. ColdRelay's 95% inbox guarantee means the infrastructure is doing its job. Use the CAN-SPAM Checker at coldrelay.com/tools/can-spam-checker and the Subject Line Generator to validate campaign content. ColdRelay's deliverability consultant (included at higher volumes) can help diagnose.