Email Deliverability with Resend: A Developer’s Honest Guide
I’ve seen 3 major email campaigns fail this quarter. All 3 made the same 5 mistakes. Getting emails into the inbox can feel like an uphill battle, especially if you’re not paying attention to email deliverability. It impacts everything from user engagement to brand reputation. So, let’s break it down.
1. Authenticate Your Emails
Why it matters: Email authentication is your first line of defense against spammers impersonating your domain. Without it, your emails could be tossed into the junk folder faster than you can say “bounce rate.”
# Setting up SPF record example
v=spf1 include:_spf.google.com ~all
# Setting up DKIM example (in DNS)
google._domainkey.yourdomain.com. 3600 IN TXT "v=DKIM1; k=rsa; p=MIGfMA0G..."
What happens if you skip it: You risk being blacklisted. I once had my entire domain flagged after one simple oversight with DKIM. Lesson learned!
2. Monitor Your Sender Reputation
Why it matters: Your sender reputation is a score that ISPs use to determine whether to deliver your emails. A bad reputation means fewer emails make it to the inbox.
# Using SenderScore API to check your score
curl -X GET "https://api.senderscore.org/v1.0/score?ip=YOUR_IP" -H "Authorization: Bearer YOUR_API_KEY"
What happens if you skip it: You may not even know your emails are being flagged, and you might as well shout into the void if your reputation is poor.
3. Clean Your Email List
Why it matters: Keeping a clean list of subscribers is crucial. If you have a bunch of dead email addresses, it drags your deliverability down. It’s like having a friend who never shows up to parties—what’s the point?
import pandas as pd
# Load email list
data = pd.read_csv('emails.csv')
# Remove duplicates
cleaned_data = data.drop_duplicates(subset=['email'])
# Save the cleaned list
cleaned_data.to_csv('cleaned_emails.csv', index=False)
What happens if you skip it: Your bounce rate will skyrocket. I once saw my open rates plummet because I had 30% invalid addresses. Not a good look.
4. Optimize Engagement
Why it matters: ISPs pay attention to how users interact with your emails. If they’re consistently ignored, your future emails are less likely to be delivered.
# Example: Implementing A/B testing with Mailchimp API
curl -X POST "https://api.mailchimp.com/3.0/campaigns" \
-H "Authorization: apikey YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{"settings": {"subject_line": "Test subject", "title": "A/B Test"}}'
What happens if you skip it: You’ll keep sending emails that nobody reads, and your deliverability will suffer as a result. Trust me: I spent months sending emails to crickets.
5. Use a Reputable Email Service Provider (ESP)
Why it matters: A good ESP like Resend or SendGrid has built-in tools to help maintain deliverability. They’ll guide you through authentication, monitoring, and more.
import resend
# Sending an email with Resend
resend.send_email(
to="[email protected]",
from_email="[email protected]",
subject="Hello!",
body="This is a test email."
)
What happens if you skip it: You could end up with a service that doesn’t prioritize deliverability. I’ve been there, and switching providers is a hassle you don’t want.
6. Monitor Bounce Rates
Why it matters: High bounce rates can be a red flag for ISPs. Monitoring helps you identify issues early.
# Check bounce rates with the Mailgun API
curl -X GET "https://api.mailgun.net/v3/YOUR_DOMAIN.com/statistics/total-bounces" \
-u 'api:YOUR_API_KEY'
What happens if you skip it: You’ll be ignoring the warning signs. I’ve lost entire campaigns because I failed to monitor bounces until it was too late.
7. Engage with Your Audience
Why it matters: Engagement isn’t just about getting users to click; it’s about creating a community. Your emails should foster a connection.
# Sample code to send a follow-up email
resend.send_email(
to="[email protected]",
from_email="[email protected]",
subject="We miss you!",
body="It's been a while since we heard from you. What can we improve?"
)
What happens if you skip it: Emails become just noise. I learned the hard way that sending generic emails without engagement leads straight to the spam folder.
8. Implement List Segmentation
Why it matters: Segmentation allows you to send targeted messages to specific groups, improving engagement and deliverability.
# Segmenting subscribers based on engagement
import pandas as pd
data = pd.read_csv('emails.csv')
active_users = data[data['last_engaged'] >= '2026-01-01']
active_users.to_csv('active_users.csv', index=False)
What happens if you skip it: You risk sending irrelevant content. Once, I sent a promotion to a segment that didn’t care, and my click-through rate tanked.
Prioritize These Steps
Here’s the order I recommend tackling these items:
- Do This Today: Authenticate Your Emails, Monitor Your Sender Reputation, Clean Your Email List, Optimize Engagement
- Nice to Have: Use a Reputable ESP, Monitor Bounce Rates, Engage with Your Audience, Implement List Segmentation
Tools for Email Deliverability
| Tool/Service | Purpose | Free Option |
|---|---|---|
| Resend | Email Sending and Management | Yes, limited usage |
| Mailgun | API for Email Sending | Yes, up to 5,000 emails |
| SendGrid | Email API and Marketing | Yes, free tier available |
| Mailchimp | Email Marketing | Yes, basic features |
| SenderScore | Reputation Monitoring | Free |
The One Thing
If you only do one thing from this list, authenticate your emails. Email deliverability depends on it. It’s the foundation of everything else. If you skip it, you’re basically throwing your emails into a black hole.
FAQ
What is email deliverability?
Email deliverability refers to the ability of an email to reach the recipient’s inbox. It’s affected by factors like authentication, sender reputation, and engagement.
How long does it take to improve email deliverability?
It varies. You might see improvements within a few days after authentication or cleaning your list, but substantial changes could take weeks.
Why are my emails going to spam?
This could be due to poor sender reputation, lack of authentication, high bounce rates, or content that triggers spam filters.
Can I test my email deliverability?
Yes, tools like Mailgun and SenderScore can help you assess your deliverability and reputation. Testing is crucial.
What role does engagement play in email deliverability?
Higher engagement rates signal to ISPs that your emails are valuable, which can improve deliverability over time. Don’t ignore it!
Data Sources
Last updated May 13, 2026. Data sourced from official docs and community benchmarks.
đź•’ Published: