How Instantly + ColdRelay Work Together
ColdRelay (Infrastructure)
ColdRelay provides the mailboxes Instantly 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.
Instantly (Sending Platform)
Instantly is one of the most popular cold email sending platforms — it handles sequences, A/B testing, unified inbox, reply detection, and campaign analytics across many mailboxes. Instantly does NOT provide the underlying email infrastructure. You bring your own mailboxes via SMTP/IMAP credentials, and Instantly orchestrates the sends across them.
Why use them together
Instantly is the brain (sequences, replies, analytics). ColdRelay is the body (mailboxes, IPs, DNS). The combination gives you a clean separation: Instantly handles campaign logic, ColdRelay handles infrastructure quality. Switching either side later is straightforward because they're loosely coupled — if you change sending platforms, the ColdRelay mailboxes still work.
Connect Instantly 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 Instantly
In Instantly, go to Email Accounts → Add New → 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 for IMAP using port 993. Instantly tests the connection and marks the mailbox as Active once it validates.
Note: Instantly's provider_code for Custom SMTP/IMAP is 1. ColdRelay's API integration with Instantly sends provider_code 1 explicitly — if you see the mailbox in a 'Reconnecting' state pointing at a Google OAuth flow, the wrong provider code was sent.
- 4
Set daily limits per mailbox
In each Instantly 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.
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 warmup in Instantly
Turn on Instantly's built-in warmup for each mailbox. Set the daily warmup limit to 2 emails, increment to 1 (sent as a STRING, not a number — this is a known Instantly v2 API quirk), and reply rate to 0.4 (a fraction representing 40%). Warmup ramps up the mailbox's reputation by exchanging emails with other Instantly warmup-network mailboxes.
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.
- 6
Configure your first campaign
In Instantly, create a campaign, paste your prospect list, write your sequence (subject lines + email bodies + follow-up cadence), and assign your ColdRelay mailboxes as the sending accounts. Instantly distributes sends across all assigned mailboxes respecting each one's daily cap.
Note: Use Instantly's spintax variations on subject lines to avoid mailbox fingerprinting. The Spintax Generator at coldrelay.com/tools/spintax-generator generates the syntax.
- 7
Monitor deliverability ongoing
Run the Email Deliverability Test weekly to verify SPF/DKIM/DMARC stay passing. 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 Instantly + ColdRelay
Daily send limits per mailbox
Set Instantly'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 Instantly users sending from shared infrastructure are sharing 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.
Instantly's unified inbox works as expected
Instantly's unified inbox aggregates replies across all your mailboxes. ColdRelay's IMAP setup is standard — Instantly polls each mailbox's IMAP at port 993 and surfaces replies normally. No special configuration needed.
Switching cost is low
If you decide Instantly isn't right and want to switch to Smartlead, EmailBison, or another sender later, your ColdRelay mailboxes work with any platform that supports custom SMTP/IMAP. You don't lose the infrastructure investment.
Domain-rotation strategy
ColdRelay caps each domain at 100-150 mailboxes for deliverability reasons. If you need 500+ mailboxes, you'll order multiple domains. Instantly handles multi-domain campaigns natively — assign mailboxes from each domain to different campaign tracks to spread risk.
ColdRelay's API integration with Instantly
ColdRelay can push new mailboxes directly into your Instantly workspace via the Instantly v2 API. This avoids the manual SMTP/IMAP copy-paste step for each mailbox. Configure your Instantly API key once in ColdRelay's Settings → Integrations, and future mailbox provisions auto-sync.
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.
Instantly
Instantly's pricing is sender-count-based. Growth plan ($37/month at the time of writing) covers ~1,000 active leads / 5,000 emails per month. Hypergrowth ($97/month) covers 25,000 active leads / 100,000 emails. Light Speed ($358/month) covers 100K leads / 500K emails. Pricing scales with campaign volume, not mailbox count.
Total monthly
A typical 200-mailbox cold email operation: ColdRelay infrastructure at ~$170/month + Instantly Hypergrowth at $97/month = ~$267/month total. At 1,000 mailboxes: ColdRelay $700/month + Instantly $358/month = ~$1,058/month. Compare against Google Workspace at $6+/mailbox/month: 200 GW mailboxes alone would be $1,200/month before Instantly's sender cost.
Common Issues + Fixes
⚠ Mailbox shows 'Reconnecting' state in Instantly pointing at Google OAuth
Wrong provider_code sent to Instantly's API. Custom SMTP/IMAP is provider_code: 1; provider_code: 2 maps to Google Workspace OAuth. ColdRelay's API integration sends provider_code 1 explicitly. If you see this state, re-sync the mailbox from ColdRelay or delete it from Instantly and re-add manually with the SMTP/IMAP credentials.
⚠ Warmup turned on in ColdRelay but not actually warming in Instantly
Instantly v2 requires a second API call to actually enable warmup — POST /api/v2/accounts/warmup/enable after the account create. If you provisioned via API and warmup is off, manually toggle it in Instantly's mailbox settings. The `increment` field must be sent as a STRING ('1', not 1) and `reply_rate` as a fraction (0.4, not 40).
⚠ 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 they all pass, check Google Postmaster Tools for the domain. The most common cause of post-authentication spam placement is exceeding the 2/day/mailbox cap in Instantly.
⚠ 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.
⚠ Instantly's unified inbox shows no replies even though prospects are replying
Instantly polls IMAP on port 993 with TLS. Verify the IMAP credentials match the ColdRelay CSV. Most commonly: the IMAP password is the same as the SMTP password but it can drift if a mailbox was reset. Re-test in Instantly's account settings (Test Connection button).
Frequently Asked Questions
Do I need ColdRelay if I already have Instantly?
Instantly is a sending platform — it doesn't provide mailboxes or DNS. You need an infrastructure provider (ColdRelay, Google Workspace, etc.) underneath it. Most Instantly 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 Instantly?
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 a free Instantly plan?
Yes, but Instantly's free plan caps you at a low active-lead and email count, which won't go far. The Instantly + ColdRelay combination really shines at Growth or Hypergrowth tier on Instantly, where the per-prospect cost becomes negligible compared to the infrastructure quality you're paying for.
Will my Instantly campaigns break if I switch to ColdRelay from another provider?
No. Switching infrastructure providers mid-campaign requires reconnecting each mailbox in Instantly (new SMTP/IMAP credentials), but campaign logic, sequences, A/B tests, and contact lists stay intact. The transition takes a few minutes per mailbox. We recommend pausing campaigns during the swap to avoid any deliverability blips.
Does ColdRelay's API push mailboxes into Instantly automatically?
Yes. Configure your Instantly v2 API key once in ColdRelay's Settings → Integrations. New mailboxes provisioned in ColdRelay are then auto-pushed into your Instantly workspace, including the warmup enable step. This avoids the manual SMTP/IMAP copy-paste for each mailbox.
What if Instantly'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.