Why US-Based IPs Matter for Cold Email Deliverability

Every email you send originates from a specific IP address, and that IP address has a geographic location. ISPs use this information as one of many signals when deciding whether to deliver your email to the inbox, promotions tab, or spam folder.

The logic is straightforward: if you are sending business emails to companies in the United States, sending from a US-based IP address looks more legitimate than sending from an IP in a country with high spam volume. ISPs maintain internal statistics on spam origination by geography, and certain regions have disproportionately high spam output.

Here is the data from our InboxKit infrastructure across 3,000+ mailboxes:

Data covers October 2025 through March 2026, sending to US-based recipients. Trust score is a composite of ISP reputation signals.

This does not mean non-US IPs cannot achieve good deliverability. They can. But US-based IPs start with a higher baseline trust score when sending to North American recipients, which means easier warmup, faster reputation building, and more consistent inbox placement over time.

We have seen this play out across our InboxKit infrastructure. When we compared identical email campaigns sent from US-based IPs versus European and Asian IPs to US recipients, the US-based IPs achieved 12-18% higher inbox placement rates on average. The difference was most pronounced with Microsoft Outlook (which tends to be more geographically sensitive) and least pronounced with Gmail (which weighs content and engagement more heavily).

For agencies and sales teams whose prospects are primarily in the US, Canada, UK, and Western Europe, US-based sending infrastructure is a deliverability advantage worth optimizing for.

Let me share specific numbers from our analysis across InboxKit accounts. This data covers 6 months of sending from October 2025 through March 2026, across approximately 3,000 mailboxes.

• US-based IPs: 87% average inbox placement
• Western European IPs (UK, Germany, Netherlands): 79% average
• Eastern European IPs: 68% average
• Asian IPs (India, Singapore): 65% average
• Other regions: 59% average

• US-based IPs: Average 12 days to reach stable reputation
• European IPs: Average 16 days
• Asian IPs: Average 19 days

• US-based IPs (reputable providers): 2.1% of accounts hit a blacklist within 90 days
• Budget international providers: 8.7% of accounts hit a blacklist within 90 days

The differences narrow when sending to recipients in the same geography as the sending IP. European IPs perform well when sending to European recipients. But since most B2B cold email targets North American businesses, US IPs have a structural advantage for the majority of senders.

Important caveat: IP location is just one factor. A US-based IP with terrible sending practices will still end up in spam. And a well-managed international IP with clean sending can achieve excellent deliverability. The IP location gives you a starting advantage, not a guarantee.

ISPs like Gmail, Outlook, and Yahoo use complex algorithms to filter email. Geographic signals are woven into these algorithms in several ways:

1. IP range reputation ISPs maintain reputation scores not just for individual IPs but for entire IP ranges (subnets). US-based cloud providers like Google Cloud, AWS (US regions), and Microsoft Azure (US regions) have high baseline reputations because they enforce strict abuse policies. Budget hosting providers in regions with less enforcement carry lower baseline scores for their entire IP ranges.

2. Sending-to-recipient geography match When the sending IP location matches the recipient's geography, ISPs view this as a positive signal. A US-based IP sending to a US-based company looks natural. A non-US IP sending exclusively to US companies can trigger additional scrutiny, especially at scale.

3. Historical abuse patterns Some IP ranges and geographies have historical patterns of spam origination. ISPs weight these patterns when evaluating new senders from those ranges. This is not about discriminating by geography. it is about statistical patterns that ISPs have observed over years of data.

4. Provider reputation Google Workspace accounts on Google's infrastructure inherit some of Google's trust. Microsoft 365 accounts benefit from Microsoft's infrastructure reputation. These are US-headquartered companies with US-based primary infrastructure, which contributes to the US IP advantage.

5. TLS and security standards US-based infrastructure providers typically enforce modern TLS standards and security practices. ISPs verify TLS certificates during email delivery, and connections from well-configured US infrastructure pass these checks cleanly.

The net effect: US-based IPs on reputable providers face a lower burden of proof with ISPs. They can build reputation faster, recover from issues more quickly, and maintain consistent deliverability with less effort.

When we built InboxKit, US-based IP infrastructure was a deliberate architectural decision, not an afterthought. Here is how it works:

Google Workspace accounts on InboxKit are provisioned on US-based IP addresses. Every mailbox at $2.99/mo sends from Google's US infrastructure. This is not the cheapest way to provision accounts. US-based provisioning costs us more than routing through other regions. but the deliverability difference justifies the investment.

Microsoft 365 accounts at $2.99/mo are similarly provisioned on US/North American infrastructure. InboxKit also offers Azure mailboxes at $30/tenant (up to 100 mailboxes) on US-based infrastructure. For teams running a mix of Google, Microsoft, and Azure accounts for provider diversity, all benefit from the US IP advantage.

What this means for your deliverability:

1. 1Faster warmup. Our accounts typically reach stable reputation 3-5 days faster than accounts on international infrastructure. This means you start sending real outreach sooner.

1. 2Higher baseline placement. New InboxKit accounts, even before warmup, see better initial inbox placement than accounts on budget international providers. The US IP reputation provides a head start.

1. 3Better Outlook deliverability. Microsoft is particularly sensitive to sending geography. US-based IPs consistently achieve 10-15% better Outlook inbox placement compared to non-US alternatives.

1. 4Lower blacklist risk. Our US-based IP ranges have clean histories and strict abuse monitoring. The 2.1% blacklist incident rate on InboxKit compares favorably to 8.7% on budget international alternatives.

1. 5Consistent performance. US infrastructure from Google and Microsoft has high uptime, fast DNS resolution, and reliable TLS. These operational factors contribute to consistent deliverability.

For agencies managing client infrastructure, the math is clear: 50 Google Workspace mailboxes on InboxKit cost $149.50/mo for mailboxes plus $150/mo for warmup ($3/mailbox/mo add-on), delivering from US IPs with InfraGuard monitoring included. The same setup on a budget international provider might cost $100/mo but achieve 15-20% lower inbox placement. which means fewer replies, fewer meetings, and less revenue for your clients.

If you are running cold email campaigns and want to measure the IP location effect, here is how to do it:

Method 1: A/B test with placement testing If you have mailboxes on different providers (some US-based, some not), send the same email content from both and run inbox placement tests. Compare the results by provider and note the differences across Gmail, Outlook, and Yahoo.

Method 2: Google Postmaster Tools comparison If you run multiple domains, check Google Postmaster Tools for each one. Domains sending from US IPs should show higher or equal reputation compared to the same sending patterns from international IPs.

Method 3: Track campaign metrics by mailbox provider In your sequencer, segment campaign results by which mailbox sent them. If some mailboxes are on InboxKit (US IPs) and others on international providers, compare open rates and reply rates between the groups.

• Inbox placement difference of 10-20% is typical when comparing US vs non-US IPs for US recipients
• Warmup time difference of 3-7 days is normal
• Reply rate differences of 5-15% (driven by the placement difference)

• Sending to US-based businesses (the majority of B2B cold email)
• Sending to corporate Outlook/Exchange environments
• Running high-volume campaigns (100+ emails/day per domain)
• Agencies managing client reputation where consistency matters

• Sending to recipients in your own country (use local IPs instead)
• Very low volume sending (under 10 emails/day)
• Sending to Gmail-only audiences (Gmail weighs engagement more than geography)

The bottom line: US-based IPs are not a silver bullet, but they provide a meaningful and measurable advantage for the typical cold email use case. At InboxKit's pricing of $2.99/mo per Google Workspace mailbox, the cost of this advantage is negligible compared to the deliverability benefit.