WHY YOUR EMAILS AREN'T BEING DELIVERED

Email Deliverability — Complete Guide

If you're doing cold outreach / lead generation, email deliverability is one of the most important things to understand.

1. What is email deliverability?

Email deliverability = the ability of your emails to successfully reach the recipient's inbox.

There are 3 different outcomes:

Outcome What it means
📥 Inbox Email reaches the main inbox
🗑️ Spam/Junk Email reaches the recipient but gets filtered
❌ Rejected/Bounced Recipient's mail server refuses the email

There's also a fourth situation:

"Missing" email → It may have been rejected, filtered, quarantined, placed in another folder, or never accepted by the recipient's server.

So delivery ≠ inbox placement.

2. Why does email go to spam?

Usually it's a combination of sender reputation + authentication + email content + recipient behavior.

A. Poor sender reputation

Email providers monitor how recipients react to your emails.

Things that hurt reputation:

  • Lots of people marking you as spam
  • Lots of bounced emails
  • Sending huge volumes suddenly
  • Very low engagement
  • Sending to old/invalid addresses
  • Recipients repeatedly deleting your emails without reading
  • Previous spam complaints from the domain/IP

Think of it like a reputation score that you can't directly see.

B. Your domain isn't properly authenticated

Your domain should normally have:

SPF

Shows which servers are allowed to send email for your domain.

DKIM

Adds a cryptographic signature proving the email wasn't altered and is authorized by your domain.

DMARC

Tells receiving servers what to do when SPF/DKIM authentication doesn't align and provides reporting.

These are DNS records.

A basic setup looks like:

Your domain
   ↓
SPF ─── Who is allowed to send?
DKIM ── Is this email authentic?
DMARC ─ What should receivers do if authentication fails?

3. Why emails "disappear"

If an email isn't visible in the inbox, don't immediately assume it's spam.

Sender-side problems

  • Email wasn't actually sent
  • Sending service failed
  • Account temporarily restricted
  • Authentication problem

Recipient-server problems

  • Hard bounce
  • Soft bounce
  • Server rejection
  • Recipient mailbox full
  • Domain doesn't exist
  • Recipient server temporarily unavailable

Filtering

  • Spam folder
  • Promotions/social tabs
  • Corporate quarantine
  • Security gateway
  • Recipient-specific filtering

Recipient-side rules

The recipient may have:

  • Filters
  • Blocked sender
  • Company security rules
  • Automatic forwarding
  • Mailbox rules

4. How to handle an outreach account

This is where people often mess up.

Before sending anything

Set up:

Domain

  • Professional domain
  • SPF
  • DKIM
  • DMARC
  • Valid MX records

Mailbox

Use a real mailbox with:

  • Real name
  • Professional signature
  • Normal profile information
  • Functional reply address

Example:

mahnoor@yourdomain.com

is generally better for professional outreach than something random like: 

sales123456@randomdomain.com

5. Don't immediately blast hundreds of emails

A new mailbox/domain has no established sending reputation.

Suddenly sending a huge number of emails can look suspicious.

Instead:

Start small → establish normal sending behavior → gradually increase volume.

Also keep your volume appropriate to the mailbox/provider's policies and your actual outreach needs.

6. Your email list matters A LOT

A terrible list can destroy deliverability.

Avoid:

  • ❌ Purchased lists of unknown quality
  • ❌ Scraped emails without validation
  • ❌ Old databases
  • ❌ Generic lists containing thousands of dead addresses
  • ❌ Sending to addresses you have reason to believe are invalid

Prefer:

  • ✅ Relevant prospects
  • ✅ Verified addresses
  • ✅ Recently obtained data
  • ✅ Low bounce rate
  • ✅ Clear targeting

For cold outreach, list quality is one of the biggest variables you control.

7. Watch your bounce rate

Two important types:

Hard bounce

The address is permanently undeliverable.

Example:

nonexistentperson@company.com

Remove it.

Soft bounce

Temporary problem.

Example:

  • Mailbox full
  • Server temporarily unavailable
  • Message temporarily rejected

Don't keep hammering the same address indefinitely.

8. Email content matters too

Spam filters look at the whole message, not just one "spam word."

Potential warning signs include:

  • Extremely aggressive sales language
  • Misleading subject lines
  • Excessive links
  • Suspicious attachments
  • Strange HTML
  • Image-heavy emails
  • URL shorteners
  • Fake "Re:" or "Fwd:"
  • Deceptive claims
  • Poor formatting

For outreach, I'd generally keep it:

short + relevant + human + easy to reply to.

Example structure:

Hi Sarah,

Saw that your agency works with SaaS companies.

I noticed [specific thing]. I had a quick idea that could help with [specific result].

Worth sending over?

— Mahnoor

Not:

🚨🔥 SPECIAL OFFER!!!
CLICK HERE NOW!!!
LIMITED TIME!!!

9. Dos ✅

DO

  • Authenticate your domain
  • Verify your email list
  • Keep bounce rates low
  • Personalize outreach
  • Keep emails concise
  • Monitor replies
  • Monitor spam complaints
  • Remove invalid addresses
  • Make unsubscribing easy where appropriate
  • Use a consistent sending identity
  • Gradually increase volume
  • Monitor domain reputation
  • Test before scaling

10. Don'ts ❌

DON'T

  • Buy random email lists
  • Blast thousands of emails immediately
  • Keep sending to bounced addresses
  • Use misleading subject lines
  • Use fake identities
  • Constantly change domains
  • Rotate domains just to evade filtering
  • Send suspicious attachments
  • Use URL shorteners unnecessarily
  • Stuff emails with links
  • Ignore spam complaints
  • Assume "sent" means "inbox"

11. How to fix an account that already has deliverability problems

First stop trying to solve everything by simply sending more emails.

Step 1 — Diagnose

Check:

  • SPF
  • DKIM
  • DMARC
  • MX
  • Bounce rate
  • Spam complaints
  • Sending volume
  • Sending patterns
  • List quality
  • Domain reputation
  • Mailbox reputation
  • Whether the issue affects Gmail, Outlook, corporate domains, etc.

Step 2 — Stop bad sending

If you're sending to a bad list:

Pause the campaign.

Clean/verify the list before continuing.

Step 3 — Remove bad addresses

Remove:

  • Hard bounces
  • Invalid addresses
  • Obvious role/trap addresses when appropriate
  • Repeatedly failing recipients

Step 4 — Fix authentication

Make sure SPF/DKIM/DMARC are correctly configured and aligned with the domain you're actually using to send.

Step 5 — Reduce problematic volume

If the account suddenly went:

20 emails/day → 500 emails/day

that's a very different sending pattern.

Bring activity back to a sustainable level rather than trying to "warm" an unhealthy account by blasting it.

Step 6 — Improve the emails

Make them:

  • Relevant
  • Short
  • Personalized
  • Low-link
  • Clear
  • Honest
  • Easy to respond to

Step 7 — Give reputation time to recover

There isn't a magic button that instantly resets sender reputation.

If the underlying problem is fixed, reputation can improve over time.

12. How to tell WHAT is actually wrong

This is an important question.

If emails are bouncing:

Investigate:

technical configuration + recipient validity + sending limits

If emails are delivered but going to spam:

Investigate:

reputation + authentication + content + engagement + complaints

If Gmail works but Outlook doesn't:

Investigate:

provider-specific filtering/reputation

If only one company doesn't receive you:

Investigate:

their corporate filtering/quarantine/blocklist

If nobody receives you:

Investigate:

domain/mailbox configuration and reputation first.

13. A simple troubleshooting checklist

You can use this every time:

EMAIL DELIVERABILITY CHECK

  • SPF configured?
  • DKIM configured?
  • DMARC configured?
  • SPF/DKIM alignment correct?
  • Domain reputation okay?
  • Mailbox reputation okay?
  • Bounce rate acceptable?
  • Spam complaints occurring?
  • Email list verified?
  • Sending volume reasonable?
  • Sudden volume increase?
  • Too many links?
  • Suspicious attachments?
  • Misleading subject?
  • Personalization/relevance?
  • Gmail affected?
  • Outlook affected?
  • Corporate domains affected?
  • Emails actually being accepted by recipient servers?

14. Questions you should ask when diagnosing an account

If you're fixing someone's outreach account, ask:

  1. What email provider are you using?
    • Google Workspace?
    • Microsoft 365?
    • Other?
  2. What domain are you sending from?
  3. How old is the domain?
  4. How old is the mailbox?
  5. How many emails/day are you sending?
  6. How quickly did you increase the volume?
  7. What's your bounce rate?
  8. Are you getting spam complaints?
  9. Are emails going to spam or actually bouncing?
  10. Which providers are affected?
    • Gmail?
    • Outlook?
    • Yahoo?
    • Business domains?
  11. Are SPF, DKIM and DMARC configured?
  12. Where did the email list come from?
  13. Is the list verified?
  14. Are you using an outreach platform?
  15. What does the email you're sending look like?
  16. Are you using links or attachments?
  17. Is this a new domain/mailbox or an established one?
  18. Has the domain/mailbox previously been used for mass outreach?
  19. What changed immediately before deliverability dropped?
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