Instead of reading thirty threads debating which inbox provider is better, I ran the test. Bought cheap and premium inboxes, ran identical campaigns, tracked everything for six months. Data speaks for itself, and it did.
Before
Started consulting with the cheapest setup I could grab. Assumed inboxes are inboxes and expensive ones just charge for the name. Got 12 domains through Mailforge at roughly $3/domain/month, warmed them through Instantly for three weeks (should've done four, more on that).
Enrichment workflow: Prospeo for finding emails, Scrubby to catch risky ones. Verification pass rate from Prospeo was solid, around 82-84% usable emails. Clay filled in gaps on a few campaigns with company-level data.
First six weeks looked okay on the surface: open rates 45-55%, reply rates 2.1%, bounce rate 3.8% - higher than I like but not catastrophic. Sending about 35 emails per inbox per day.
But around week seven things started sliding. Open rates dropped to 28-33% on four inboxes. One got flagged and stopped delivering entirely. By month three I'd lost three of twelve to deliverability issues, the remaining nine were inconsistent. Some days 50% opens, others 22% on the same sequence.
Bounce rate crept up to 4.7%. Reply rate across the portfolio dropped to 1.4%. I was booking maybe 8-9 meetings a month for clients when I'd projected 14-16.
Worst part was the unpredictability - couldn't tell clients with any confidence what to expect. One client nearly churned because their campaign went from six replies in a week to one on the same list, same copy, same everything. Only variable was inbox deliverability, and I had no real control.
Also made a mistake with warmup timing: three weeks felt fine when I had established domains with history. Turns out fresh domains from a cheap provider need more. Lost those three inboxes to figure that out.
After
Month three I tested properly. Kept six surviving Mailforge inboxes running and bought six new inboxes through Maildoso at ~$4.50/domain/month. Not a huge price difference, but Maildoso handles DNS and authentication setup - saved me time and contributed to better deliverability out of the gate.
Switched to four weeks of warmup minimum on the new inboxes. Ran them through Instantly warmup pool, didn't send a single cold email until day 28. The Mailforge ones kept running as-is for comparison.
Ran the same sequences, same lists, same copy across both sets for the next three months. Same verticals, same ICPs, same send times. Prospeo handled enrichment on all - so list quality variable controlled. Tracked opens, replies, bounces, and meetings booked per set.
Results after three months side-by-side:
Mailforge (cheap ones that survived): open rate average 37.2%, reply rate 1.8%, bounce rate 4.1%, one more inbox died during this period - down to five by the end. Meetings booked across those five over three months: 19.
Maildoso inboxes: open rate average 52.6%, reply rate 3.1%, bounce rate 1.9%, zero inbox deaths, zero deliverability flags. Meetings booked across six over three months: 34.
That's almost double the meetings from the Maildoso set. And consistency was night and day - they stayed within a tight band week to week. Could actually predict output for clients, which is the whole point when you're charging them.
Cost breakdown: Mailforge setup cheaper per inbox, but factoring in the three that died, plus time troubleshooting DNS issues and revenue lost from bad deliverability months... it wasn't cheaper. Spent roughly $216 over six months on Mailforge (including replacements). About $162 on Maildoso for the same period. And the Maildoso set generated probably $4k-5k more in client revenue because of higher meeting volume.
Caveats: this isn't perfectly clean science. Got better at writing copy over the six months, so later campaigns (skewing toward Maildoso) might have benefited. List building improved too - by month four, bounce rates dropped across both sets. But the deliverability gap was real and consistent even when controlling for those. Maildoso inboxes landed in primary more often - spot-checked with a seed list tool, hit primary on Gmail about 73% of the time vs 51% for Mailforge.
Other changes that helped but are separate: dropped send volume to 28 per inbox per day - felt like leaving money on the table but improved everything. Added a two-day delay between steps instead of one. Stopped sending on Mondays entirely - data showed Monday reply rates were consistently 30-40% lower than Tuesday-Thursday.
Also switched from HubSpot free to Attio around month four for CRM - HubSpot overkill for a solo operation, Attio cleaner. Not related to the inbox test but people ask about my stack.
The thing I keep coming back to: spent months treating inboxes as a commodity when they're actually infrastructure. Bad infrastructure has compounding costs that don't show up on your credit card - they show up in missed meetings, client churn, and your own stress. The $1.50/month difference per inbox between cheap and mid-tier is nothing compared to the cost of one dead inbox supporting a client campaign.
Is premium always worth it? Depends on volume and how much variance you can absorb. If you're sending from 50+ inboxes and expect 10-15% attrition, cheap might make sense. But for a solo operation or small agency where every inbox matters... yeah, the premium tier paid for itself multiple times over.
Anyway, the data is what it is. I still keep two Mailforge inboxes around for testing new sequences before rolling them out to client campaigns. But everything client-facing runs through Maildoso now and has for about four months.
