RampCORE

ESP throttling is when your email service provider deliberately slows or limits your sending rate. It happens when you exceed daily limits, spike volume too quickly, or trigger abuse-detection systems.

Microsoft 365 enforces a 10,000 email/day tenant limit — exceed it and you get NDR code 4.7.500. Google Workspace caps at 2,000/day for standard accounts. SendGrid uses a reputation-based system where new accounts start throttled and earn higher limits over time.

The key insight: throttling is not punishment — it's protection. ESPs throttle to prevent their IP ranges from being blacklisted by receiving servers. When RampCORE builds a schedule that stays below 80% ESP capacity, it's leaving headroom for transactional email spikes and natural volume fluctuations.

Inbox providers (Gmail, Outlook, Yahoo) maintain reputation scores for every sending domain. A brand new domain has no history — it starts at neutral, which ISPs treat as suspicious until proven otherwise.

New domains (0-30 days) get the tightest scrutiny. Google typically takes 5-7 days of consistent low-volume sending before upgrading a domain's trust level. Microsoft needs 7-14 days. During this window, even small volume spikes can trigger spam classification.

Mature domains (1+ year) have earned accumulated trust. They can handle faster ramps and higher volumes because ISPs have months of positive data. RampCORE adjusts starting volumes by up to 30% based on domain maturity — a mature domain might start at 65 emails/day while a new domain starts at 20.

DMARC (Domain-based Message Authentication, Reporting & Conformance) is critical during warmup because it tells ISPs how to handle emails that fail SPF or DKIM authentication checks.

Before warmup: Set DMARC to p=none with reporting enabled. This lets you monitor authentication failures without impacting delivery. Many warmup issues are actually DKIM alignment problems that only surface under DMARC reporting.

During warmup (days 1-14): Keep p=none and monitor daily DMARC aggregate reports. Fix any alignment issues immediately. After 14 days of clean data, move to p=quarantine.

Post-warmup: Graduate to p=reject for maximum protection. This tells ISPs to block any email claiming to be from your domain that fails authentication — protecting both your reputation and your recipients.

Bounce codes tell you exactly why an email failed to deliver. During warmup, monitoring these codes is more valuable than open rates.

4xx (Soft Bounces) — Temporary failures. The server accepted the connection but deferred delivery. Common during throttling. 421 = "try again later" (rate limiting). 450 = "mailbox busy". These usually resolve on retry.

5xx (Hard Bounces) — Permanent failures. 550 = "user unknown" (bad address). 551 = "user not local" (forwarding issue). 553 = "authentication required". Remove hard bounce addresses immediately — continued sending to known-bad addresses destroys sender reputation.

Critical threshold: If total bounce rate exceeds 5% on any single day during warmup, pause sending for 24 hours and reduce volume by 30% when resuming. If hard bounces exceed 2%, your list has quality issues that need cleaning before continuing the ramp.

These are two different processes that people frequently confuse. Domain warmup establishes sender reputation for a new or dormant domain. Tools like Instantly, Lemwarm, and Warmbox automate this by exchanging emails between a network of mailboxes — simulating natural sending patterns. This takes 2-4 weeks.

Campaign ramp is what happens after your domain is warm. You now need to gradually increase the volume of your actual marketing emails through your ESP. Even with a perfectly warm domain, jumping from 0 to 50,000 campaign emails will trigger ESP throttling and ISP velocity filters.

Think of it this way: domain warmup is getting your driver's license. Campaign ramp is learning to drive on the highway. You need both, in that order. RampCORE handles the second part — building ESP-aware volume ramp schedules for your marketing campaigns.

Before starting any warmup or campaign ramp, configure these free monitoring tools:

Google Postmaster Tools — Shows your domain reputation with Gmail (bad/low/medium/high), spam rate, authentication results, and delivery errors. Set up at postmaster.google.com. Takes 24-48 hours to start showing data.

Microsoft SNDS — Smart Network Data Services shows how Microsoft views your sending IPs. Reports on spam traps, complaints, and filtering status. Register at sendersupport.olc.protection.outlook.com.

MXToolbox — Free blacklist monitoring. Check your sending IPs and domain against 100+ blacklists. Set up alerts for immediate notification if you land on a list during your ramp.

Your ESP Dashboard — Every ESP provides bounce rate, complaint rate, and delivery metrics. Set up webhook notifications for bounce rates exceeding 2% and complaint rates exceeding 0.1%.