ColdSire Inbox Warmer for Niche B2B Agencies

Boutique B2B agencies running cold outreach for clients in verticals like legal and healthcare face a recurring, painful bottleneck: their emails land in spam. The HN threads in this brief show the depth of the problem. One company reports being hit with what looks like a keyword blacklist on Microsoft 365, where messages to clients simply vanish. Another self-hosting operator with a decade-old clean IP, correct DKIM and SPF, and enrollment in Microsoft's Junk Mail Reporting Program still gets rejected outright. And Mailgun just slashed its free tier from 10k to 625 emails per month, squeezing the smaller players who were leaning on generic infrastructure. ColdSire Inbox Warmer is a SaaS that spins up pre-warmed cold email inboxes with industry-specific warm-up sequences tuned to agency verticals. Instead of a one-size-fits-all warm-up like the general tooling (Warmy.io appears in the community signal as a reference point, and Instantly.ai is the main competitor), ColdSire tailors the ramp schedule, sending cadence, and content fingerprint to the language patterns and sender reputation realities of a given vertical. The core insight: legal and healthcare outreach carries vocabulary that trips keyword-sensitive filters, and the HN blacklist complaint points directly at this. A warm-up sequence that accounts for vertical-specific wording and recipient-domain behavior is the wedge. MVP: provision warmed inboxes on managed domains, run automated inbox-to-inbox warm-up with vertical-aware content, and give agencies a deliverability dashboard showing placement rates per inbox before they ever load a real campaign. Revenue is a per-inbox monthly subscription with tiers by number of seats and verticals, the standard model Instantly already validates. GTM starts where the pain is loudest: the HN and YouTube audiences actively discussing cold email open rates and deliverability tooling, plus direct outreach to boutique agencies (eating our own dog food). Growth loops: agencies managing multiple clients add inboxes as they win accounts, and visible deliverability wins become a referral story inside tight-knit agency communities.