Deliverability

Reputation is everything

Mailbox providers decide where a message goes largely on the reputation of the domain and IP address it comes from. Reputation is built from how recipients react: opens and replies help; bounces, spam complaints and ignored mail hurt.

Authentication (SPF, DKIM, DMARC) is the entry ticket — it lets providers attribute reputation to your domain at all. Everything after that is about sending mail people want.

Bounces

A hard bounce is a permanent failure: the address doesn’t exist or the domain can’t receive mail. Never retry a hard bounce — keep sending to dead addresses and providers treat you as a spammer with a bought list.

A soft bounce is temporary — a full mailbox or a server that is briefly unavailable. The message is retried automatically. Keep your hard-bounce rate well under 2%; above 5% most providers start throttling or blocking you.

Spam complaints

Every time a recipient clicks "Report spam", the provider counts it against you. Gmail asks senders to stay below a 0.1% complaint rate and never exceed 0.3%.

Most complaints come from people who don’t remember signing up or can’t find the unsubscribe link. Make the sender name recognisable, send what people asked for, and make unsubscribing effortless.

List hygiene

• Never buy or rent lists — they are full of dead addresses and spam traps.
• Validate addresses at signup to catch typos and disposable inboxes.
• Use double opt-in for marketing lists.
• Stop mailing people who haven’t opened anything in months, or send them a re-engagement email first.

Warm up new domains

A brand-new domain has no reputation, and sudden volume from an unknown sender looks like spam. Start with your most engaged recipients and a few hundred messages a day, then roughly double the volume every few days while bounce and complaint rates stay low.

Transactional mail — receipts, password resets — warms a domain naturally because recipients expect and open it.

Check it yourself