Backend Development › Email & Notifications

Email Deliverability

Bounces, spam complaints, sender reputation and staying out of spam folders.

Backend Engineer · Mid-level Tech Entrepreneur · Growth

Also known as: email deliverability, deliverability, inbox placement

Email deliverability is whether the mail you send actually reaches recipients’ inboxes, rather than their spam folder or a blocklist. It’s decided by mailbox providers (Gmail, Outlook, …) using signals about your sender reputation, authentication, sending behaviour and content — not by anything you control directly.

The main levers:

Authentication — SPF, DKIM and DMARC (see SPF/DKIM/DMARC) prove you’re allowed to send as your domain and that the message wasn’t altered. Misconfiguration is a common deliverability killer.
Sender reputation — built from complaint rates, bounces, and engagement (opens, replies, marks-as-spam). A domain/IP with a bad reputation gets filtered.
List hygiene — sending to invalid or unengaged addresses (high bounce/complaint rates) damages reputation. Remove hard bounces and inactive recipients.
Consent and engagement — mail people asked for; spam complaints are the strongest negative signal.
Volume and warmup — a sudden spike in volume from a new IP/domain looks like spam; ramp up gradually.

authenticate (SPF/DKIM/DMARC) + clean list + consent + steady volume + good engagement
→ inbox.   Any one badly off → spam.

The classic mistakes:

Ignoring authentication. Without SPF/DKIM/DMARC, providers are suspicious (and may reject outright). Set them up before sending at volume.
Buying or scraping lists. Recipients who didn’t opt in mark you as spam, cratering reputation. Never do it.
Ignoring bounces and complaints. Continuing to send to hard-bounced addresses damages reputation; process bounces and complaints promptly.
A big blast from a cold domain. A new sender sending 100k emails at once is instantly suspicious. Warm up gradually.
Overloaded or misleading content. Spammy phrasing, image-only emails, or mismatched “from”/links get filtered. Match content to expectation.
Using a shared IP carelessly. On a shared sending service, other senders’ reputation can affect you; transactional senders often use dedicated IPs.
Not monitoring. Deliverability problems appear as falling opens and rising bounces/complaints. Track them; don’t discover spam-foldering from a user complaint.

How to stay deliverable: authenticate your domain, send only to people who asked, keep the list clean, warm up new sending, honour bounces and complaints, and monitor open/bounce/complaint rates. Deliverability is a relationship with mailbox providers — technical setup plus respectful sending behaviour. See sending email and transactional vs marketing email.