How Mailshake + ColdRelay Work Together
ColdRelay (Infrastructure)
ColdRelay provides the mailboxes Mailshake 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.
Mailshake (Sending Platform)
Mailshake is a sales engagement and cold email platform — it handles multi-step sequences, A/B testing, lead catcher (reply detection), and native integrations with Salesforce, HubSpot, and Pipedrive. Mailshake does NOT provide the underlying email infrastructure. You bring your own mailbox via SMTP credentials (through its Email Sender Setup flow), and Mailshake orchestrates the sends and CRM sync on top.
Why use them together
Mailshake is the brain (sequences, lead catcher, CRM sync). ColdRelay is the body (mailboxes, IPs, DNS). The combination gives you a clean separation: Mailshake handles sales engagement workflow and CRM integration, 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 with any tool that supports custom SMTP.
Connect Mailshake 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
Add each mailbox via Mailshake's Email Sender Setup
In Mailshake, go to Senders → Add Sender → Connect Other Email Provider (Custom SMTP). For each ColdRelay mailbox, paste the SMTP host (box.YOURDOMAIN.com), SMTP port (587), username (the full email address), and password from the ColdRelay CSV. Mailshake also needs IMAP configured for reply tracking — paste the IMAP host with port 993 and matching credentials. Mailshake validates the connection and marks the sender as Connected once it passes.
Note: Mailshake's Email Sender Setup explicitly supports custom SMTP/IMAP — you don't need Google Workspace or Microsoft 365 OAuth. The 'Connect Other Email Provider' path is the one to use for ColdRelay mailboxes.
- 4
Set daily limits per sender
In each Mailshake sender'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. Mailshake distributes campaign sends across all enabled senders.
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
Configure warmup separately
Mailshake does not include a built-in warmup network the way some competitors do. ColdRelay mailboxes ship reputation-ready (the Azure tenant + dedicated IP isolation gives you a clean start), so a dedicated warmup tool isn't strictly required, but it's still recommended for the first 2 weeks of active sending. Use a third-party warmup service connected to the same SMTP/IMAP credentials, with a 2/day warmup cap so total daily activity stays at 2 outbound + 2 warmup = 4/day MAX.
Note: If you do run external warmup, point it at the IMAP host on port 993 with the same credentials. Verify Mailshake's lead catcher still picks up real replies — most warmup tools tag their messages so they can be filtered out of reply analytics.
- 6
Build your first sequence
In Mailshake, create a Campaign, paste your prospect list (CSV upload or CRM sync from Salesforce/HubSpot), write your sequence (initial email + follow-ups with delays), and assign your ColdRelay senders as the sending accounts. Mailshake distributes sends across all assigned senders, respecting each one's daily cap. Use AB Testing on subject lines and email bodies to optimize over time.
Note: Use spintax variations on subject lines to avoid mailbox fingerprinting. The Spintax Generator at coldrelay.com/tools/spintax-generator generates the syntax Mailshake accepts.
- 7
Wire up CRM sync (optional)
If you use Salesforce, HubSpot, or Pipedrive, configure Mailshake's native CRM integration so replies and engagement events sync as activities/tasks against the right contact records. The integration is set up once at the workspace level (Integrations menu) and applies to all campaigns. ColdRelay's infrastructure has no role here — the CRM sync runs entirely inside Mailshake.
Note: Lead catcher routes positive replies to a sales rep automatically. Test the routing rules before launching at volume — Mailshake's defaults sometimes treat out-of-office replies as positive responses.
- 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). Mailshake's own deliverability dashboard shows bounce rate, open rate, and reply rate per sender so you can spot a degrading mailbox early.
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 Mailshake + ColdRelay
Daily send limits per sender
Set Mailshake's per-sender 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 Mailshake users sending from shared infrastructure (Google Workspace, generic SMTP relays) 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.
Mailshake's strength is sales engagement, not infrastructure
Mailshake's value sits in lead catcher, AB testing, and the native Salesforce/HubSpot/Pipedrive integrations — features built for sales teams that run cold outbound as part of a broader CRM workflow. Pair that with ColdRelay underneath and you get enterprise-grade infrastructure powering an enterprise-grade sales engagement layer, without paying enterprise SaaS pricing on either side.
Switching cost is low
If you decide Mailshake isn't right and want to switch to Instantly, Smartlead, or another sender later, your ColdRelay mailboxes work with any platform that supports custom SMTP/IMAP. You don't lose the infrastructure investment — only the sequence and reporting history inside Mailshake itself.
Domain-rotation strategy
ColdRelay caps each domain at 100-150 mailboxes for deliverability reasons. If you need 500+ mailboxes, you'll order multiple domains. Mailshake handles multi-domain campaigns natively — assign senders from each domain to different campaign tracks (or different sales reps) to spread risk and keep per-domain volume in safe ranges.
Warmup is BYO
Unlike some sending platforms, Mailshake doesn't bundle a warmup network. ColdRelay mailboxes are reputation-ready out of the box, but for the first 2 weeks of active sending we recommend pairing with a third-party warmup tool. Keep the combined daily volume (outbound + warmup) at or below 4/day/mailbox.
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.
Mailshake
Mailshake is priced per user per month, billed annually. The Email Outreach tier (around $59/user/month) covers cold email sequences, AB testing, and basic integrations. The Sales Engagement tier (around $99/user/month) adds lead catcher, advanced CRM sync, power phone dialer, and LinkedIn touches. Pricing scales with sales-rep headcount, not mailbox count.
Total monthly
A typical 200-mailbox cold email operation with 2 sales reps: ColdRelay infrastructure at ~$170/month + Mailshake Sales Engagement at ~$198/month (2 users × $99) = ~$368/month total. At 1,000 mailboxes with 4 reps: ColdRelay $700/month + Mailshake $396/month = ~$1,096/month. Compare against Google Workspace at $6+/mailbox/month: 200 GW mailboxes alone would be $1,200/month before Mailshake's per-seat cost.
Common Issues + Fixes
⚠ Mailshake sender shows 'Connection Failed' after entering ColdRelay SMTP credentials
Mailshake's SMTP test connects to the host on port 587 with STARTTLS. Verify the host is exactly box.YOURDOMAIN.com (not the bare domain) and the username is the full email address. The most common cause is a typo in the password — re-copy from the ColdRelay CSV. If the test still fails, run a quick telnet/openssl handshake against the host to confirm the SMTP server is responding, then contact ColdRelay support.
⚠ Lead catcher not picking up replies
Mailshake's lead catcher polls IMAP on port 993 with TLS. Verify the IMAP credentials match the ColdRelay CSV — 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 the sender's settings. Also confirm the sender is enabled for the campaign in question; disabled senders don't poll for replies.
⚠ 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 Mailshake — verify the per-sender daily limit is set correctly.
⚠ CRM sync from Mailshake to Salesforce/HubSpot creating duplicate contacts
This is a Mailshake-side issue, not an infrastructure issue. In Mailshake's CRM integration settings, enable 'match by email address' as the dedup key before sync. If duplicates still appear, check whether the prospect CSV uploaded to the campaign had email-case inconsistencies (john@example.com vs John@Example.com). ColdRelay's infrastructure plays no role here.
⚠ 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 use Mailshake?
Mailshake is a sales engagement platform — it doesn't provide mailboxes or DNS. You need an infrastructure provider (ColdRelay, Google Workspace, etc.) underneath it. Most Mailshake 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 Mailshake?
For cold email at any scale beyond a handful of mailboxes: yes. Google Workspace charges $6+/mailbox/month and shares 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 — and Mailshake's custom-SMTP path makes the swap trivial.
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 through Mailshake, you need 500 senders connected. The Mailbox Calculator at coldrelay.com/tools/mailbox-calculator lets you input your target volume and gives you the exact mailbox count + pricing tier.
Does Mailshake provide warmup the way other sending tools do?
No. Mailshake focuses on sequences, lead catcher, and CRM integration — it doesn't bundle a warmup network. ColdRelay mailboxes are reputation-ready out of the box thanks to the dedicated Azure tenant and dedicated IPs, but for the first 2 weeks of active sending we recommend pairing with a third-party warmup tool pointed at the same SMTP/IMAP credentials, capped at 2/day so combined daily activity stays under 4/day/mailbox.
Can Mailshake's Salesforce or HubSpot integration sync ColdRelay-sent activity to the CRM?
Yes. The CRM integration is entirely Mailshake-side — Mailshake records the send/open/reply events as they happen and pushes them to Salesforce or HubSpot as activities or tasks against the matching contact record. ColdRelay's only role is delivering the email; Mailshake handles the engagement tracking and CRM sync layer on top.
Will my Mailshake campaigns break if I switch to ColdRelay from another provider?
No. Switching infrastructure providers mid-campaign requires reconnecting each sender in Mailshake (new SMTP/IMAP credentials via the Email Sender Setup flow), but campaign logic, sequences, AB tests, and prospect lists stay intact. The transition takes a few minutes per sender. We recommend pausing campaigns during the swap to avoid any deliverability blips.
What if Mailshake'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.