Overview — What Each Platform Does
ColdRelay
ColdRelay provisions Microsoft 365 mailboxes on isolated Azure tenants with dedicated IPs. Per-mailbox pricing: $1 (1-199), $0.85 (200-999), $0.70 (1K-4,999), $0.55 (5K+). Each mailbox sends 2 outbound + 2 warmup = 4 emails/day. Includes automated SPF/DKIM/DMARC, no warmup wait, a 95% inbox guarantee, 14-day money-back, 50-mailbox minimum, and 60-minute setup.
Mailscale
Mailscale is a self-serve cold-email-inbox SaaS that runs its own SMTP servers and IP pools rather than reselling Microsoft 365 or Google Workspace. Plans are inbox-capped: Solopreneur $79/mo (up to 15 inboxes, ~$5.27 each), Business $119/mo (up to 50 inboxes, ~$2.38 each), Enterprise $249/mo (up to 200 inboxes, ~$1.25 each), and an Unlimited tier from $1,000/mo that adds dedicated IPs and a deliverability specialist. Mailscale recommends 30-50 emails/inbox/day, offers a 7-day free trial, claims 3,000+ customers, and backs setups with a 95-100% deliverability promise (free domain replacement if placement drops below 80%).
Feature Comparison
| Feature | ColdRelay | Mailscale |
|---|---|---|
| Mailbox Technology | ✓ Microsoft 365 on Azure — trusted-sender reputation with Outlook, Gmail, and corporate filters | Self-hosted SMTP servers and IP pools — purpose-built but not M365/Workspace, so receiving filters treat it as a third-party sender |
| IP Strategy | ✓ Dedicated IPs on isolated Azure tenants — your reputation is yours alone at every plan tier | Shared IP pools on Solopreneur/Business/Enterprise; dedicated IPs only on Unlimited ($1,000+/mo) |
| Pricing Model | Per-mailbox: $1 down to $0.55 — pay for the inboxes you actually use | Inbox-capped plans: $79 / $119 / $249 / $1,000+ — pay the tier even if you don't fill it |
| Effective $/Mailbox at 50 | ✓ $50/mo flat (50 mailboxes × $1) | $119/mo Business plan caps at 50 inboxes (~$2.38 each) |
| Effective $/Mailbox at 200 | ✓ $170/mo total — $0.85 per mailbox | $249/mo Enterprise plan, capped at 200 inboxes — ~$1.25 per mailbox if fully saturated |
| Effective $/Mailbox at 1,000+ | ✓ $700/mo (1,000 × $0.70), drops to $0.55 at 5K | Unlimited tier from $1,000/mo — flat fee, less granular |
| Daily Send Limit / Mailbox | 2 outbound + 2 warmup = 4/day — conservative cap that protects long-term reputation | Recommends 30-50/day per inbox — higher per-mailbox throughput, higher per-mailbox burn risk |
| Deliverability Guarantee | 95% inbox placement, 14-day money-back if missed | 95-100% deliverability promise + free domain replacement if placement drops below 80% |
| Free Trial | No free trial — 14-day money-back guarantee covers risk | ✓ 7-day free trial on all paid plans |
| Setup Speed | Automated provisioning — infrastructure live in 60 minutes | Self-serve provisioning — inboxes spin up quickly inside the platform |
| Minimum Commitment | 50 mailboxes ($50/mo) | ✓ Solopreneur plan at $79/mo (15 inboxes) |
| Maturity & Social Proof | Newer entrant, infrastructure-led positioning | ✓ 3,000+ customers, established self-serve SaaS |
Where ColdRelay Wins
ColdRelay's biggest structural advantage is the mailbox itself: Microsoft 365 on isolated Azure tenants with dedicated IPs. Mailscale runs its own SMTP and shares IP pools across customers on every plan except the $1,000+/mo Unlimited tier — meaning your sender reputation is partly dictated by whoever else is on the pool. Below 200 mailboxes ColdRelay's per-mailbox pricing also lands cheaper than Mailscale's tiers ($50 vs $119 at 50 mailboxes), and at 1,000+ mailboxes the $0.70/$0.55 volume rates beat Mailscale's flat Unlimited fee. The 95% inbox guarantee with 14-day money-back is a more concrete commitment than 'free domain replacement if placement drops below 80%.'
Where Mailscale Wins
Mailscale wins on early-stage frictionlessness: 7-day free trial, $79/mo entry tier, 15 inboxes for a single solopreneur, and 3,000+ customers worth of UX polish. Per-inbox cost is lower than ColdRelay specifically in the 50-200 mailbox band on the Enterprise plan ($1.25/inbox vs ColdRelay's $1.00-$0.85). Mailscale's recommended 30-50 emails/inbox/day is also significantly more throughput per mailbox than ColdRelay's conservative 4/day — useful if you have fewer mailboxes and need to push more volume through each.
✓ Choose ColdRelay If…
Choose ColdRelay if you want Microsoft 365 mailboxes on dedicated IPs and isolated tenants — the same trusted-sender stack that corporate filters expect — without paying $1,000+/mo for the privilege. Best for agencies running client-isolated infrastructure, sales teams that treat deliverability as production-critical, and operations scaling past 1,000 mailboxes where volume pricing compounds.
Choose Mailscale If…
Choose Mailscale if you're a solopreneur or small team that wants a 7-day free trial, a $79/mo entry point, and the operational simplicity of self-hosted SMTP with no Microsoft 365 setup. Mailscale also makes sense if you specifically need higher throughput per mailbox (30-50/day) and can accept shared IP pools on everything below the $1,000+ Unlimited tier.
The Verdict
Mailscale and ColdRelay solve the same problem with fundamentally different stacks: Mailscale runs its own SMTP on shared IP pools and sells inbox-capped SaaS tiers; ColdRelay resells Microsoft 365 on isolated Azure tenants with dedicated IPs and sells per-mailbox. If you need a low-friction trial under 50 inboxes, Mailscale's $79 plan wins. If deliverability is a production requirement and you'll cross 50 mailboxes, choose ColdRelay.
Frequently Asked Questions
Does Mailscale use Microsoft 365 or Google Workspace?
Neither. Mailscale explicitly states they run their own SMTP servers and IP pools rather than reselling Microsoft 365 or Google Workspace. ColdRelay provisions Microsoft 365 mailboxes on isolated Azure tenants, which is the stack receiving filters trust most.
Are Mailscale IPs dedicated or shared?
Shared on Solopreneur, Business, and Enterprise plans. Dedicated IPs are only included on Mailscale's Unlimited tier (starts at $1,000/mo). ColdRelay includes dedicated IPs on every plan from 50 mailboxes up.
Which is cheaper at 100 mailboxes?
ColdRelay: 100 × $1.00 = $100/mo. Mailscale: $249/mo Enterprise plan (caps at 200 inboxes, so you'd be paying for headroom you don't use). ColdRelay is cheaper at this volume.
Which is cheaper at 200 mailboxes?
ColdRelay: 200 × $0.85 = $170/mo. Mailscale: $249/mo Enterprise plan (saturated 200-inbox cap = ~$1.25/inbox). ColdRelay wins on absolute cost; Mailscale's per-inbox rate only beats ColdRelay if you fill the cap and need >4 sends/day per mailbox.
Does Mailscale offer a free trial?
Yes — 7 days on all paid plans. ColdRelay doesn't have a free trial but offers a 14-day money-back guarantee tied to the 95% inbox placement promise.