How EmailBison + ColdRelay Work Together
ColdRelay (Infrastructure)
ColdRelay provides the mailboxes EmailBison 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.
EmailBison (Sending Platform)
EmailBison is a cold email sending platform with a strong focus on AI-powered campaign generation, sequences, integrated warmup, reply detection, and a master inbox that unifies replies across all connected mailboxes. EmailBison does NOT provide the underlying email infrastructure. You bring your own mailboxes via custom SMTP/IMAP credentials, and EmailBison orchestrates sending and reply handling across them.
Why use them together
EmailBison is the brain (AI campaigns, sequences, master inbox). ColdRelay is the body (mailboxes, IPs, DNS). The pairing gives you a clean separation of concerns: EmailBison handles campaign logic and reply orchestration, ColdRelay handles infrastructure quality. Because each side is loosely coupled to the other through standard SMTP/IMAP, switching platforms later is straightforward — the ColdRelay mailboxes keep working regardless of which sender sits on top of them.
Connect EmailBison 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 automated provisioning spins up 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 EmailBison
In EmailBison, open the Email Accounts section and choose Add Account → Custom SMTP / IMAP. For each ColdRelay mailbox, paste its SMTP host (box.YOURDOMAIN.com), SMTP port (587 with STARTTLS), SMTP username (the full email address), and the password from the ColdRelay CSV. Repeat for IMAP using port 993 with SSL. EmailBison runs a connection test and marks the account as Active once both SMTP and IMAP validate.
Note: If EmailBison rejects the connection, double-check that the SMTP/IMAP host matches the box.YOURDOMAIN.com value in your ColdRelay CSV — not the bare YOURDOMAIN.com. The mail-server hostname is the box subdomain.
- 4
Set daily limits per mailbox
In each EmailBison 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 EmailBison
Turn on EmailBison's built-in warmup for each mailbox. Set the daily warmup limit to 2 emails and a healthy reply rate (around 40%). Warmup ramps mailbox reputation by exchanging emails with other mailboxes in EmailBison's warmup network, helping new domains build a positive sending history before live campaigns scale up.
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. The per-mailbox total cap is 2 outbound + 2 warmup = 4/day MAX.
- 6
Build your first AI-assisted campaign
In EmailBison, create a new campaign, paste your prospect list, and use the AI campaign builder to draft your sequence (subject lines + email bodies + follow-up cadence). Assign your ColdRelay mailboxes as the sending accounts. EmailBison distributes sends across all assigned mailboxes while respecting each one's daily cap.
Note: Use spintax variations on subject lines to reduce mailbox fingerprinting. The Spintax Generator at coldrelay.com/tools/spintax-generator outputs the syntax EmailBison expects.
- 7
Configure the master inbox for replies
EmailBison's master inbox aggregates replies from every connected mailbox into a single view. Make sure IMAP is enabled and connected for each ColdRelay mailbox (port 993, SSL) — the master inbox polls these connections to surface replies, positive intent, and out-of-office responses. No special ColdRelay configuration is needed beyond the standard IMAP credentials.
Note: If replies don't appear, the most common cause is an IMAP connection that has drifted (mailbox password reset, port blocked). EmailBison flags these in the account list — re-test the connection from inside the mailbox settings.
- 8
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 EmailBison + ColdRelay
Daily send limits per mailbox
Set EmailBison'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 senders on shared cold-email infrastructure share IP reputation with random other accounts — a bad actor on the same IP damages everyone's deliverability. With ColdRelay your IP reputation is entirely your own.
Master inbox + IMAP reliability
EmailBison's master inbox is one of its standout features, and it depends on a stable IMAP connection to every connected mailbox. ColdRelay's IMAP is standard (port 993, SSL) and stays up — but if you ever rotate a mailbox password, refresh the credential inside EmailBison so the master inbox keeps pulling replies.
AI campaigns still need human deliverability discipline
EmailBison's AI campaign builder accelerates copy production, but no AI can save you from infrastructure issues (bad DNS, exceeded send caps, weak domain reputation). Treat the AI as a copywriting accelerator, not a deliverability tool — the infrastructure layer underneath has to be solid for any AI-generated copy to land in primary.
Switching cost is low
If you decide EmailBison isn't the right sender and want to switch to Instantly, Smartlead, or another platform later, your ColdRelay mailboxes work with any platform that supports custom SMTP/IMAP. You don't lose the infrastructure investment — only the campaign-platform configuration moves.
Domain-rotation strategy
ColdRelay caps each domain at 100-150 mailboxes for deliverability reasons. If you need 500+ mailboxes you'll order multiple domains. EmailBison handles multi-domain setups natively — assign mailboxes from each domain to different campaign tracks to spread risk and avoid any single domain dominating your send mix.
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.
EmailBison
EmailBison's pricing is plan-based, tiered by connected mailbox count and feature access (AI campaigns, master inbox, warmup, team seats). Plans scale from small operators connecting a handful of mailboxes up to agency tiers supporting hundreds of mailboxes and multi-workspace setups. Check emailbison.com for current plan pricing — it moves over time, so we don't quote specific dollar figures here.
Total monthly
A typical 200-mailbox cold email operation pairs ColdRelay infrastructure at ~$170/month with an EmailBison agency-tier plan sized for that mailbox count. At 1,000 mailboxes: ColdRelay $700/month + EmailBison's largest tier appropriate to that mailbox count. Compare against Google Workspace at $6+/mailbox/month: 200 GW mailboxes alone would be $1,200/month before EmailBison's sender cost — the infrastructure-layer savings are where the real economics come from.
Common Issues + Fixes
⚠ EmailBison rejects the SMTP/IMAP connection during account add
Verify the SMTP/IMAP host is the box.YOURDOMAIN.com value from the ColdRelay CSV — not the bare YOURDOMAIN.com. SMTP port is 587 (STARTTLS), IMAP port is 993 (SSL). The username is the full email address, and the password is the one issued in the ColdRelay CSV. If the connection still fails, re-pull the credentials in ColdRelay (mailboxes can be re-keyed if needed) and re-add the account in EmailBison.
⚠ Warmup turned on in EmailBison but the mailbox isn't actually warming
Open the mailbox in EmailBison and confirm warmup is enabled at both the account level and the daily-limit level (daily warmup limit > 0). If warmup is on but no warmup emails are flowing in or out, give it 24 hours — warmup networks ramp gradually. If after 48 hours there's still no activity, test the SMTP and IMAP connections from inside EmailBison's account settings to confirm both directions still work.
⚠ 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 EmailBison, or running AI-generated copy with too-aggressive subject lines or link density.
⚠ Master inbox shows no replies even though prospects are replying
EmailBison's master inbox polls each mailbox's IMAP on port 993 with SSL. 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 the IMAP connection in EmailBison's mailbox settings (Test Connection). If IMAP is healthy but replies still don't surface, check the campaign's reply-detection settings to make sure they're enabled.
⚠ 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.
Frequently Asked Questions
Do I need ColdRelay if I already have EmailBison?
EmailBison is a sending platform — it doesn't provide mailboxes or DNS. You need an infrastructure provider (ColdRelay, Google Workspace, etc.) underneath it. Many EmailBison 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 EmailBison?
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 EmailBison's AI campaign builder with ColdRelay mailboxes?
Yes. The AI campaign builder is a copy-and-sequence layer inside EmailBison — it doesn't care what infrastructure sits underneath. ColdRelay mailboxes connect via standard SMTP/IMAP, and EmailBison's AI runs the same way regardless of which provider the mailboxes come from. The infrastructure quality affects deliverability, not which copy tools you can use on top.
Will my EmailBison campaigns break if I switch to ColdRelay from another provider?
No. Switching infrastructure providers mid-campaign requires reconnecting each mailbox in EmailBison (new SMTP/IMAP credentials), but campaign logic, sequences, AI templates, 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 while the cutover happens.
Does ColdRelay integrate with EmailBison via API to auto-add mailboxes?
If EmailBison exposes a public mailbox-add API, ColdRelay can push new mailboxes into your EmailBison workspace automatically — the same way our Instantly integration pushes mailboxes via the Instantly v2 API. If you're an EmailBison customer and want this set up, check ColdRelay's Settings → Integrations for the current EmailBison option, or contact support for status. Until that's live, you'll connect mailboxes manually with the CSV credentials.
What if EmailBison'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, AI copy that pattern-matches to spam) 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 the campaign side.