Email deliverability checklist and sender reputation guide
Learn how to improve email deliverability, protect sender reputation, and keep campaigns out of spam with a practical checklist and troubleshooting tips.
Email deliverability tends to get attention only after something breaks. The campaign goes out, the numbers look fine at first glance, and then open rates sag, or complaints creep up. Usually the issue is not one dramatic failure, it is a few small ones that were ignored.
This guide covers what deliverability actually means, how it differs from delivery, what affects sender reputation, and the checks worth making before the next send.
Quick checklist
If you need the short version, start here.
- Authenticate every sending domain with SPF, DKIM, and DMARC
- Keep marketing and transactional traffic on separate subdomains
- Pick an IP strategy that matches your volume and cadence
- Warm up new domains and IPs slowly
- Start with engaged recipients
- Remove hard bounces, spam complaints, and inactive contacts
- Keep content clear, useful, and easy to scan
- Watch delivery rate, bounce rate, complaint rate, and inbox placement
- Check Google Postmaster Tools, SNDS, and blocklist status regularly
What email deliverability is
Email deliverability is the chance that your message reaches the inbox instead of drifting into spam or promotions.
Mailbox providers look at a mix of signals before they decide where to place a message. They review your authentication, your reputation, your list quality, your content, and the way you send. A message can be accepted by the receiving server and still miss the inbox.
That is why deliverability matters. It is not enough for the send to s쳮d. The message has to show up where people will actually see it.
Email delivery vs email deliverability
These terms get mixed up all the time.
| Term | What it means |
|---|---|
| Delivery | The receiving server accepted your email |
| Deliverability | The email reached the inbox, not spam or promotions if you can avoid it |
A Gmail server can accept your email and still place it in spam. That is delivery without deliverability.
The distinction sounds small until you are trying to explain why a campaign underperformed. The platform says the send s쳮ded, but the audience never saw it in the right place.
What affects email deliverability
Mailbox providers do not use one signal. They use a cluster of them.
Authentication
SPF, DKIM, and DMARC tell mailbox providers that your message came from a sender you control.
If these records are missing or broken, everything else has a harder time.
Sender reputation
Sender reputation is the trust score mailbox providers assign to your domain and IP address. It changes as your sending pattern changes.
They look at bounce rate, complaint rate, engagement, list quality, sending consistency, authentication, and blocklist status. A healthy reputation gives you a better shot at the inbox, and a damaged one makes every send harder than it should be.
List quality and engagement
These two usually travel together.
A clean list tells mailbox providers that people want your email. A stale list tells a different story – old contacts, invalid addresses, spam traps, and people who have not opened anything in months all drag down performance.
Engagement matters just as much. Opens, clicks, replies, and deletes all send a signal, when people interact with your mail, inbox providers notice, when they ignore it or mark it as spam, they notice that too.
Sending consistency
Mailbox providers like predictable senders.
Big volume spikes, long gaps between campaigns, and erratic content can all look suspicious. A steady rhythm gives providers something easier to trust.
Content quality
The message itself still matters.
Spam filters watch for broken HTML, weak subject lines, heavy image use, and language that feels too pushy or too vague. If the email reads like it was written for filters instead of people, that usually shows up in the results.
Blocklists and inbox placement
If your IP or domain lands on a blocklist, deliverability can fall quickly. The same goes for poor inbox placement even when the send itself technically s쳮ds.
That is why regular checks matter. Catch the problem early, and you have a much better chance of fixing it before the reputation damage spreads.
Your email deliverability checklist
Use this as a working checklist, not a one-time setup task.
1. Set up the account correctly
Choose an email service provider that fits your volume, your technical requirements, and the level of support you expect.
We saw a significant 168% global increase in email traffic on our platform in 2025. (Source: Messaging trends report)
Look for:
- Strong deliverability performance
- Clear reporting
- Easy integration
- A deliverability support team
- Email Deliverability Center for visibility into reputation and data that might affect your inbox placement
- Deliverability Agent for guided troubleshooting and faster fixes
- A setup that lets you separate traffic types
If you send both promotional and transactional mail, keep them apart. Separate subdomains help protect one stream when the other has a problem.
Examples:
- offers.brand-domain.com for marketing
- transactional.brand-domain.com for transactional mail
Avoid parked domains, cousin domains, and no-reply sender addresses when you can. They do little for trust and even less for engagement.
2. Authenticate every sending domain
Set up SPF, DKIM, and DMARC before you send at scale.
Then check the records with trusted tools. Many teams use MXToolbox or similar validators to catch setup issues early. For Gmail traffic, register the domain in Google Postmaster Tools so you can track reputation and spam rate.
Treat authentication as maintenance, not a one-off job. Recheck it after DNS changes, migrations, and new domain launches.
3. Choose the right IP strategy
Dedicated IPs and shared IPs both make sense in different situations.
| Option | Best for | Watch out for |
|---|---|---|
| Dedicated IP | High volume, time-sensitive sending, tighter control | Needs a warm-up period and regular volume |
| Shared IP | Lower volume, faster launch, lower cost | Reputation depends on other senders too |
Dedicated IPs work well when you send often and want more control over reputation. Shared IPs work well when you are starting out, sending less frequently, or want speed over control.
If you choose dedicated IPs, expect a warmup period of about 6 to 8 weeks based on volume.
4. Warm up slowly
Warmup teaches mailbox providers that your sending is legitimate.
Start small and increase volume gradually. Send first to the people most likely to engage, while keeping the cadence steady. Do not jump from a quiet launch to a huge send.
A global ride-sharing company once ran into deliverability problems on Microsoft email services for more than 550 million recipients because it could not throttle sends properly. Infobip used its Email API warmup feature to onboard 20 IP addresses and split the volume across them. That protected delivery speed and reduced the risk of overwhelming inbox providers.
Warmup works best when the list is clean and the sending pattern is calm.
5. Clean your list before you scale
List quality matters as much as setup.
Keep the list healthy by doing the basics well:
- Build your list organically
- Use double opt-in where possible
- Validate addresses before sending
- Remove hard bounces
- Suppress spam complaints
- Remove inactive subscribers
- Let people update preferences instead of forcing them to unsubscribe
- Segment based on behavior and interest
If someone has not engaged in a long time, stop sending them the same volume. Re-engage them first or move them to a lower-frequency stream.
6. Write content people want to open
Mailbox providers reward engagement, so write for the reader first.
Good email content is relevant, clear, easy to scan, mobile-friendly, and honest about the offer.
Avoid:
- Overused spam words
- Too many exclamation points
- ALL CAPS
- URL shorteners
- Too many images
- Heavy blocks of text with no hierarchy
The subject line should make a real promise. The body copy should keep it. The call to action should make the next step obvious.
7. Monitor the right metrics
Deliverability problems usually show up in the numbers before they show up anywhere else.
Watch these metrics regularly:
- Delivery rate
- Bounce rate
- Open rate
- Click-to-open rate
- Unsubscribe rate
- Spam complaints
As a practical benchmark, Infobip tracks delivery rates at 97% to 99%, bounce rates at 2% to 3% or lower, and spam complaints below 0.2%.
When those numbers shift, do not guess. Check the cause.
Common deliverability problems and how to fix them
When inbox placement slips, work through the problem from the top down.
| Problem | What usually causes it | What to do |
|---|---|---|
| Low inbox placement | Authentication gaps, weak reputation, poor list quality | Check SPF, DKIM, and DMARC. Clean the list. Send first to engaged users |
| Sudden open rate drop | More mail going to spam or promotions, blocklist issues, volume spikes | Check inbox placement, review recent sending changes, and test blocklists |
| Rising spam complaints | Irrelevant content, too much frequency, poor segmentation | Reduce cadence, segment better, and give subscribers more control |
| Blocked domain or IP | Reputation damage or blocklist listing | Pause risky sends, investigate the cause, and request delisting where needed |
| High bounce rate | Bad data, poor validation, stale contacts | Validate addresses, remove invalid records, and suppress hard bounces |
| Missing authentication | DNS errors or incomplete setup | Recheck SPF, DKIM, and DMARC, then test again before resuming volume |
Sometimes the fastest fix is also the least glamorous one. Pause the send if you need to, protect what reputation you have left, then rebuild it slowly.
How to monitor deliverability over time
One report does not tell the whole story. Deliverability needs regular attention.
Use Google Postmaster Tools
Google Postmaster Tools helps you monitor Gmail performance. It shows domain reputation, spam rate, authentication status, and delivery errors.
If Gmail traffic matters to your business, this should be part of your weekly review.
Use SNDS for Microsoft traffic
Microsoft SNDS gives you visibility into how Microsoft sees your IP and domain reputation. It also helps you spot complaint spikes, spam trap hits, and volume changes.
Check blocklists regularly
Use blocklist tools to see whether your IP or domain has been listed. Common checks include MXToolbox, Hetrixtools, Bulk Black List, and Multirbl.
Review inbox placement
Inbox placement tools help you see whether your email lands in the inbox or gets filtered out.
That matters because delivery rate alone can flatter the numbers. If the message lands in spam, the send technically worked and the campaign still failed.
A real-world example
A fintech company with 4 million users ran into Gmail throttling and bounce issues. The causes were plain once the team looked closely.
They had started sending at high volume without proper warmup. The list quality was weak and hard bounces were high. New domains and IPs saw sudden spikes. The content also needed work because it lacked a clear CTA and did not follow email best practices.
Infobip helped the team fix it step by step.
- Auto alerts flagged high hard bounce rates
- The team paused sending to stop further damage
- List validation cleaned the data
- A custom warmup plan focused on recent engagers and double opt-in users
- Four new domains helped the team scale safely
- The team improved content and deliverability guidance
The result was lower hard bounce rates, better soft bounce handling, and stronger delivery performance.
That is the pattern worth copying. Fix the foundation first. Then scale.
How Infobip helps teams stay ahead of deliverability issues
Keeping deliverability healthy takes more than best practices. Teams need visibility, context, and a fast path from alert to action.
Email Deliverability Center
Email Deliverability Center gives teams a central place to watch deliverability health. It pulls together the signals that matter most, including reputation, IP and domain reputation, blocklist status, spamtraps, traffic issues, and the trends that show whether performance is steady or starting to slip.
It helps when you want to:
- Spot changes early
- Review deliverability health in one place
- Track whether a domain or IP is getting better or worse
- Share a clearer picture with marketing, operations, and technical teams
Deliverability Agent
Deliverability Agent helps teams move from “something looks wrong” to a practical next step. The agent can perform content analysis, helping customers create emails that have a lower likelihood of ending up in spam. It supports troubleshooting by turning deliverability symptoms into a more focused investigation.
It helps when you need to:
- Narrow down the likely cause of a drop in inbox placement
- Check whether the issue points to authentication, list quality, content, or reputation
- Reduce the time spent guessing
- Decide what to fix first
Used together, they help teams spot deliverability shifts early and act before inbox placement slips.
Start improving deliverability
If your campaigns are not reaching the inbox the way they should, start with the basics.
Check your authentication. Review your domain and IP strategy. Clean your list. Warm up gradually. Watch the numbers that matter. Small fixes in the right places usually have an outsized effect on inbox placement and sender reputation.
Frequently asked questions
Email deliverability is your ability to land in the inbox. It goes beyond sending success and looks at where the message ends up after the mailbox provider reviews it.
Authentication, sender reputation, list quality, engagement, content quality, sending consistency, and blocklist status all shape deliverability.
A strong program keeps delivery rates near 97% to 99%, bounce rates under 2% to 3%, and spam complaints below 0.2%. The exact target depends on your audience, content, and sending model.
Authenticate your domain, send to engaged contacts first, keep your list clean, warm up slowly, and stay consistent with your sending pattern.
A warmup usually takes 6 to 8 weeks, depending on volume and consistency. High-volume senders may need more time if the audience is cold or the domain is new.
Delivery means the receiving server accepted the email. Deliverability means the email reached the inbox instead of spam or promotions.
![Mobile phone mockup displaying an email message titled ‘A quick note from [Company Name]’ sent from ‘Atypical.’ The email welcomes the recipient, explains account management on behalf of a creditor, outlines how often messages will be sent, reassures about safe communication, and includes contact and preference update details. The phone is centered on a dark background with abstract pink, orange, and white shapes.](https://cdn-web.infobip.com/uploads/2026/03/blog-email-collections-header-image-600x333.png)
