Email has the highest ROI of any marketing channel. $36 for every $1 spent. Yet most startups treat it as an afterthought - bulk blasts, no personalization, landing in spam folders. This skill covers transactional email that works, marketing automation that converts, deliverability that reaches inboxes, and the infrastructure decisions that scale. Use when: keywords, file_patterns, code_patterns.
Email has the highest ROI of any marketing channel. $36 for every $1 spent.
Yet most startups treat it as an afterthought - bulk blasts, no personalization,
landing in spam folders.
This skill covers transactional email that works, marketing automation that
converts, deliverability that reaches inboxes, and the infrastructure decisions
that scale.
Principles
Transactional vs Marketing separation | Description: Transactional emails (password reset, receipts) need 100% delivery.
Marketing emails (newsletters, promos) have lower priority. Use separate
IP addresses and providers to protect transactional deliverability. | Examples: Good: Password resets via Postmark, marketing via ConvertKit | Bad: All emails through one SendGrid account
Permission is everything | Description: Only email people who asked to hear from you. Double opt-in for marketing.
Easy unsubscribe. Clean your list ruthlessly. Bad lists destroy deliverability. | Examples: Good: Confirmed subscription + one-click unsubscribe | Bad: Scraped email list, hidden unsubscribe, bought contacts
Deliverability is infrastructure | Description: SPF, DKIM, DMARC are not optional. Warm up new IPs. Monitor bounce rates.
Deliverability is earned through technical setup and good behavior. | Examples: Good: All DNS records configured, dedicated IP warmed for 4 weeks | Bad: Using free tier shared IP, no authentication records
One email, one goal | Description: Each email should have exactly one purpose and one CTA. Multiple asks
means nothing gets clicked. Clear single action. | Examples: Good: "Click here to verify your email" (one button) | Bad: "Verify email, check out our blog, follow us on Twitter, refer a friend..."
Timing and frequency matter | Description: Wrong time = low open rates. Too frequent = unsubscribes. Let users
set preferences. Test send times. Respect inbox fatigue. | Examples: Good: Weekly digest on Tuesday 10am user's timezone, preference center | Bad: Daily emails at random times, no way to reduce frequency
Patterns
Transactional Email Queue
Queue all transactional emails with retry logic and monitoring
When to use: Sending any critical email (password reset, receipts, confirmations)
Automatically handle bounces to protect sender reputation
When to use: Processing bounce and complaint webhooks
switch (bounceType) {
case 'hard':
await markEmailInvalid(email);
break;
case 'soft':
await incrementBounceCount(email);
if (count >= 3) await markEmailInvalid(email);
break;
case 'complaint':
await unsubscribeImmediately(email);
break;
}
React Email Components
Build emails with reusable React components
When to use: Creating email templates
import { Button, Html } from '@react-email/components';
export default function WelcomeEmail({ userName }) {
return (
<Html>
<h1>Welcome {userName}!</h1>
<Button href="https://app.com/start">
Get Started
</Button>
</Html>
);
}
Preference Center
Let users control email frequency and topics
When to use: Building marketing or notification systems
Preferences:
☑ Product updates (weekly)
☑ New features (monthly)
☐ Marketing promotions
☑ Account notifications (always)
Respect preferences in all sends
Required for GDPR compliance
Sharp Edges
Missing SPF, DKIM, or DMARC records
Severity: CRITICAL
Situation: Sending emails without authentication. Emails going to spam folder.
Low open rates. No idea why. Turns out DNS records were never set up.
Symptoms:
Emails going to spam
Low deliverability rates
mail-tester.com score below 8
No DMARC reports received
Why this breaks:
Email authentication (SPF, DKIM, DMARC) tells receiving servers you're
legit. Without them, you look like a spammer. Modern email providers
increasingly require all three.
Situation: Password resets going to spam. Using free tier of email provider.
Some other customer on your shared IP got flagged for spam.
Your reputation is ruined by association.
Symptoms:
Transactional emails in spam
Inconsistent delivery
Using same provider for marketing and transactional
Why this breaks:
Shared IPs share reputation. One bad actor affects everyone. For
critical transactional email, you need your own IP or a provider
with strict shared IP policies.
Recommended fix:
Transactional email strategy:
Option 1: Dedicated IP (high volume)
Get dedicated IP from your provider
Warm it up slowly (start with 100/day)
Maintain consistent volume
Option 2: Transactional-only provider
Postmark (very strict, great reputation)
Includes shared pool with high standards
Separate concerns:
Transactional: Postmark or Resend
Marketing: ConvertKit or Customer.io
Never mix marketing and transactional
Not processing bounce notifications
Severity: HIGH
Situation: Emailing same dead addresses over and over. Bounce rate climbing.
Email provider threatening to suspend account. List is 40% dead.
Symptoms:
Bounce rate above 2%
No webhook handlers for bounces
Same emails failing repeatedly
Why this breaks:
Bounces damage sender reputation. Email providers track bounce rates.
Above 2% and you start looking like a spammer. Dead addresses must
be removed immediately.
Recommended fix:
Bounce handling requirements:
Hard bounces:
Remove immediately on first occurrence
Invalid address, domain doesn't exist
Soft bounces:
Retry 3 times over 72 hours
After 3 failures, treat as hard bounce
Track bounce rate by campaign
Alert if bounce rate exceeds 1%
Missing or hidden unsubscribe link
Severity: CRITICAL
Situation: Users marking as spam because they cannot unsubscribe. Spam complaints
rising. CAN-SPAM violation. Email provider suspends account.
Symptoms:
Hidden unsubscribe links
Multi-step unsubscribe process
No List-Unsubscribe header
High spam complaint rate
Why this breaks:
Users who cannot unsubscribe will mark as spam. Spam complaints hurt
reputation more than unsubscribes. Also it is literally illegal.
CAN-SPAM, GDPR all require clear unsubscribe.
Option to reduce frequency instead of full unsubscribe
Sending HTML without plain text alternative
Severity: MEDIUM
Situation: Some users see blank emails. Spam filters flagging emails. Accessibility
issues for screen readers. Email clients that strip HTML show nothing.
Symptoms:
No text/plain part in emails
Blank emails for some users
Lower engagement in some segments
Why this breaks:
Not everyone can render HTML. Screen readers work better with plain text.
Spam filters are suspicious of HTML-only. Multipart is the standard.
Recommended fix:
Always send multipart:
await resend.emails.send({
from: '[email protected]',
to: '[email protected]',
subject: 'Welcome!',
html: '<h1>Welcome!</h1><p>Thanks for signing up.</p>',
text: 'Welcome!\n\nThanks for signing up.',
});
Auto-generate text from HTML:
Use html-to-text library as fallback
But hand-crafted plain text is better
Plain text should be readable:
Not just HTML stripped of tags
Actual formatted text content
Sending high volume from new IP immediately
Severity: HIGH
Situation: Just switched providers. Started sending 50,000 emails/day immediately.
Massive deliverability issues. New IP has no reputation. Looks like spam.
Symptoms:
New IP/provider
Sending high volume immediately
Sudden deliverability drop
Why this breaks:
New IPs have no reputation. Sending high volume immediately looks
like a spammer who just spun up. You need to gradually build trust.
Send to Gmail/Microsoft first (they set reputation)
Maintain consistent volume
Don't spike and drop
During warm-up:
Monitor deliverability closely
Check feedback loops
Adjust pace if issues arise
Emailing people who did not opt in
Severity: CRITICAL
Situation: Bought an email list. Scraped emails from LinkedIn. Added conference
contacts. Spam complaints through the roof. Provider suspends account.
Maybe a lawsuit.
Symptoms:
Purchased email lists
Scraped contacts
High unsubscribe rate on first send
Spam complaints above 0.1%
Why this breaks:
Permission-based email is not optional. It is the law (CAN-SPAM, GDPR).
It is also effective - unwilling recipients hurt your metrics and
reputation more than they help.
Recommended fix:
Permission requirements:
Explicit opt-in:
User actively chooses to receive email
Not pre-checked boxes
Clear what they are signing up for
Double opt-in:
Confirmation email with link
Only add to list after confirmation
Best practice for marketing lists
What you cannot do:
Buy email lists
Scrape emails from websites
Add conference contacts without consent
Use partner/customer lists without consent
Transactional exception:
Password resets, receipts, account alerts
do not need marketing opt-in
Emails that are mostly or entirely images
Severity: MEDIUM
Situation: Beautiful designed email that is one big image. Users with images
blocked see nothing. Spam filters flag it. Mobile loading is slow.
No one can copy text.
Symptoms:
Single image emails
No text content visible
Missing or generic alt text
Low engagement when images blocked
Why this breaks:
Images are blocked by default in many clients. Spam filters are
suspicious of image-only emails. Accessibility suffers. Load times
increase.
Recommended fix:
Balance images and text:
60/40 rule:
At least 60% text content
Images for enhancement, not content
Always include:
Alt text on every image
Key message in text, not just image
Fallback for images-off view
Test:
Preview with images disabled
Should still be usable
Example:
<img
src="hero.jpg"
alt="Save 50% this week - use code SAVE50"
style="max-width: 100%"
/>
<p>Use code <strong>SAVE50</strong> to save 50% this week.</p>
Missing or default preview text
Severity: MEDIUM
Situation: Inbox shows "View this email in browser" or random HTML as preview.
Lower open rates. First impression wasted on boilerplate.
Symptoms:
View in browser as preview
HTML code visible in preview
No preview component in template
Why this breaks:
Preview text is prime real estate - appears right after subject line.
Default or missing preview text wastes this space. Good preview text
increases open rates 10-30%.
Recommended fix:
Add explicit preview text:
In HTML:
<div style="display:none;max-height:0;overflow:hidden;">
Your preview text here. This appears in inbox preview.
<!-- Add whitespace to push footer text out -->
‌ ‌ ‌ ‌
</div>
With React Email:
<Preview>
Your preview text here. This appears in inbox preview.
</Preview>
Best practices:
Complement the subject line
40-100 characters optimal
Create curiosity or value
Different from first line of email
Not handling partial send failures
Severity: HIGH
Situation: Sending to 10,000 users. API fails at 3,000. No tracking of what sent.
Either double-send or lose 7,000. No way to know who got the email.
Symptoms:
No per-recipient send logging
Cannot tell who received email
Double-sending issues
No retry mechanism
Why this breaks:
Bulk sends fail partially. APIs timeout. Rate limits hit. Without
tracking individual send status, you cannot recover gracefully.
