Mission Inbox review. Cold email infrastructure with a focus on deliverability

mission_review · 2026-04-03 · 1,890 views

I've been hearing about Mission Inbox in a few cold email communities so I decided to test them properly. Ordered 12 Google Workspace inboxes and ran them for 45 days alongside my existing PuzzleInbox accounts.

What Mission Inbox does well: They're focused on cold email infrastructure specifically, not general email hosting. DNS setup (SPF, DKIM, DMARC) was configured on delivery. The accounts arrived as legitimate Google Workspace accounts. Their documentation on best practices is solid.

Where they fall short: No pre-warming option. You're on your own for warmup which means 14 to 21 days of dead time before you can send. No Outlook 365 inboxes available. If you want to match sender to recipient platform (Google to Gmail, Outlook to Outlook recipients), you'll need a second provider for Microsoft accounts. Support response time averaged about 18 hours by email.

Deliverability results: After warmup, inbox placement landed around 74% to 78% on GlockApps. Respectable numbers. Reply rates on test campaigns were about 2.9%. Not bad at all, but noticeably below what I get on PuzzleInbox pre-warmed accounts (4.1% reply rate, 87%+ inbox placement).

Bottom line: Mission Inbox is a serviceable cold email infrastructure provider. They do the basics right. But PuzzleInbox's pre-warmed option saves you 3 weeks of warmup time, their Outlook availability lets you run a dual platform strategy, and their support responds in minutes instead of hours. If cold email infrastructure is your revenue engine, those differences add up fast.