Email Deliverability¶
Email deliverability refers to the ability of your emails to successfully reach recipients' inboxes rather than being filtered, rejected, or marked as spam.
Deliverability is influenced by five key factors:
| Factor | Summary |
|---|---|
| Authentication | Proving your identity to mailbox providers |
| Sending reputation | Your track record as a sender |
| Content quality | How relevant and trustworthy your emails look |
| Bounce management | How you handle undeliverable addresses |
| Spam compliance | Respecting consent and making unsubscribing easy |
Sending Reputation¶
Your sending reputation is your "credit score" with mailbox providers. It is built over time based on your sending behavior and how recipients engage with your emails. Poor reputation leads to spam placement or outright blocking.
What Influences Reputation¶
| Signal | Impact |
|---|---|
| High spam complaint rate | ❌ Negative |
| High bounce rate | ❌ Negative |
| Sending to inactive users | ❌ Negative |
| Sudden volume spikes | ❌ Negative |
| Strong open & click rates | ✅ Positive |
| Consistent sending cadence | ✅ Positive |
Content Quality¶
Mailbox providers analyze email content to determine spam likelihood and user relevance. Well-structured, relevant emails are less likely to be filtered.
Write Natural, Relevant Copy¶
- Focus on value for the recipient.
- Avoid aggressive sales language.
- Personalize where possible.
Maintain a Healthy Design Structure¶
- Use a balanced text-to-image ratio — avoid image-only emails.
- Include a clear and visible CTA.
- Optimize for mobile.
- Use clean HTML with no broken code.
Things to Avoid¶
| Avoid | Why |
|---|---|
| ALL CAPS subject lines | Triggers spam filters |
| Excessive punctuation ("!!!") | Triggers spam filters |
| Spam-trigger phrases | Triggers spam filters |
| URL shorteners (e.g., bit.ly) | Seen as suspicious by mailbox providers |
| Too many external links | Lowers content trustworthiness |
Bounce Management¶
Bounces occur when an email cannot be delivered. There are two types, each requiring a different response.
Hard Bounce — Permanent Failure¶
Caused by an invalid email address or non-existent domain.
Action: Remove the address from your database immediately. Continuing to send to hard-bounced addresses damages your reputation.
Soft Bounce — Temporary Failure¶
Caused by a full mailbox or a temporary server issue.
Action: Retry sending. If the same address soft-bounces 3–5 times, suppress it.
Spam Avoidance & Complaint Management¶
Make Unsubscribing Easy¶
- Keep the unsubscribe link visible and accessible.
- Honor unsubscribe requests immediately.
- Never hide or complicate the process.
Segment by Engagement¶
- Reduce sending frequency to inactive users.
- Run re-engagement campaigns before removing contacts.
- Remove non-responders after a defined period (e.g. 90–180 days).
Never¶
- Use purchased or scraped lists.
- Send without explicit consent.