Email Infrastructure Built for SaaS
Whether you're sending onboarding emails to your first 100 users or transactional notifications to millions, sendmsg.io grows with your product, with built-in reputation protection at every stage.
An email API for SaaS is infrastructure that handles transactional and promotional email on behalf of a software platform, providing reliable delivery, reputation management, and developer-friendly integration. SaaS companies need email infrastructure that scales with their user base, isolates sending reputation per client or activity, and warms up new domains without manual oversight. sendmsg.io is designed for this use case. It provides a REST API with SDKs for Node.js, Python, PHP, and Go, plus SMTP relay for legacy systems. Each sending activity gets its own reputation tracking, so a bad campaign by one team or tenant does not damage deliverability for the rest. The Reputation Shield system monitors ISP signals across all sending and adjusts volume and speed on its own. Smart Warmup handles new domain onboarding with progressive volume increases based on actual engagement data from ISPs.
Why SaaS Email is Different
SaaS companies have unique email requirements that generic ESPs don't address. You need both transactional reliability and promotional reach, growing volumes that track with product adoption, multiple sending domains for different product lines, and sender reputation that directly affects whether your users can access their accounts.
Deliverability Affects User Experience
When your OTP emails land in spam or don't arrive at all, users can't log in. When password reset links are delayed, support tickets pile up. For SaaS products, email deliverability is a product quality issue, not just a marketing concern.
Volume Grows Unpredictably
A successful product launch or viral moment can multiply your email volume overnight. Infrastructure that handles 10,000 emails a day needs to handle 100,000 the next without DNS reputation damage or throttling by major ISPs.
Reputation is Shared Risk
A single poorly targeted promotional campaign can tank your domain reputation, which then affects the deliverability of every transactional email sent from that domain. Without isolation, marketing mistakes become authentication failures.
Transactional + Promotional in One Platform
Most SaaS teams end up using one provider for transactional emails and another for marketing campaigns. The reason is simple: they don't trust that a bad promotional send won't affect their OTP delivery.
sendmsg.io solves this with per-activity reputation isolation. Each campaign activity is tracked independently: the throttling hierarchy flows from Activity to Domain to Client. A promotional activity with higher-than-expected bounces triggers Adaptive Protection for that specific activity, without touching the delivery speed or reputation of your transactional traffic.
- Separate reputation tracking per activity, domain, and client
- Transactional emails always get priority queuing
- Promotional issues trigger isolated protection, not system-wide throttling
- Single API and dashboard for all email types
Spring Sale campaign rate is adjusted due to bounce signals. Transactional emails continue at full speed, unaffected.
SaaS Email Use Cases
From the first welcome email to re-engagement campaigns, every message type your SaaS product needs.
User Onboarding
Welcome emails, getting started guides, feature walkthroughs. First impressions that set the tone for your user relationship and drive activation rates.
Authentication
OTP codes, two-factor verification, password resets, email confirmation links. Time-sensitive messages that need sub-second delivery and near-perfect inbox placement.
Billing & Invoicing
Payment receipts, subscription renewals, failed payment alerts, upgrade notices. Financial communications that users expect in their inbox, not their spam folder.
Product Updates
Feature announcements, changelog digests, maintenance notices, version updates. Keep your users informed about what's new without overwhelming their inbox.
Re-engagement
Inactive user campaigns, win-back sequences, trial expiration reminders. Targeted campaigns to bring users back, with reputation safeguards that protect your transactional traffic.
Built-in Reputation Management for Growing Teams
You don't need a dedicated deliverability engineer on your team. Reputation Shield runs continuously, watching ISP response signals and adjusting your sending behavior to maintain healthy delivery rates.
Smart Warmup as You Grow
New sending domains are warmed up through graduated volume stages that match ISP expectations. When your product grows and you add new domains, they're brought online safely without manual warmup plans.
Adaptive Rate Limiting
Sending rate adjusts live based on signals from receiving mail servers. If Gmail starts throttling, your sending speed to Gmail addresses decreases while other ISPs continue at full rate.
Automatic Protection
If something goes wrong (a bad list import, a template rendering error causing bounces), Adaptive Protection kicks in before your domain reputation is damaged. Sending slows, then recovers gradually once signals are clean.
Domain Health Dashboard
A single health score from 0 to 100 for every sending domain. See bounce rates, block signals, engagement metrics, and sending volume trends. Know where you stand without digging through log files.
Integrate in Minutes, Not Days
A clean REST API, official SDKs for the languages your team already uses, and detailed documentation. Send your first email within minutes of creating an API key.
- SDKs for Node.js, Python, PHP, and Go
- RESTful API with consistent resource models
- Template engine with dynamic variables
- Webhook events for live delivery tracking
- Detailed API logs for debugging
const sendmsg = require('@sendmsg/sdk');
// Send a welcome email when a new user signs up
async function sendWelcomeEmail(newUser) {
const response = await sendmsg.emails.send({
to: newUser.email,
template: 'welcome-onboarding',
variables: {
name: newUser.name,
loginUrl: `https://app.yourproduct.com/login`,
trialDays: 14,
},
});
console.log('Sent:', response.messageId);
}Scales With Your Product
Start on the free tier today. Upgrade as your product grows. Infrastructure and reputation management scale with your volume.
0 - 10K emails/month
- Full API access from day one
- Smart Warmup for new domains
- Basic delivery analytics
- Email and community support
10K - 100K emails/month
- Advanced engagement analytics
- Multiple sending domains
- A/B testing for campaigns
- Webhook event streaming
100K - 1M+ emails/month
- Dedicated sending infrastructure
- Custom volume limits
- Priority support with SLA
- Custom integration assistance
Live Analytics Dashboard
See exactly what's happening with your email as it happens. Delivery rates, engagement metrics, bounce tracking, and domain health scores, all in one dashboard that updates as events come in.
- Delivery & engagement metrics
Open rates, click rates, bounce rates, and complaint rates tracked per campaign and domain.
- Domain Health Score
A 0-100 score for each sending domain that reflects live ISP reputation signals.
- Volume trends
Sending volume over time with week-over-week comparison. Spot anomalies before they become problems.
- Event search
Search delivery events by recipient, message ID, campaign, or tag. Debug delivery issues in seconds.
Build Better SaaS Email
Stop worrying about email deliverability and start building. Full reputation protection included on every plan.