Sender Reputation & Domain Warm-up
Whether your emails reach the inbox or the spam folder depends less on the plugin and more on your sender reputation – how mailbox providers (Gmail, Outlook, Apple) judge mail from your domain. This guide covers the practical steps to build and keep a good reputation: authentication, warming up a new domain, and list hygiene. It’s provider-agnostic; for the Mailgun-specific DNS records see MailGun Setup.
The three things that decide inbox placement
- Authentication – can the receiver prove the mail really came from you?
- Reputation – does mail from your domain/IP usually get opened, or marked as spam?
- List quality – are you sending to real people who want it, or to stale/scraped addresses?
Get these right and you land in the inbox. Get them wrong and even perfect content goes to spam.
1. Authentication – do this first
Before sending any volume, set up the three DNS records that prove your mail is legitimate:
- SPF – lists which servers may send for your domain.
- DKIM – cryptographically signs each message so the receiver can verify it wasn’t altered or forged.
- DMARC – tells receivers what to do with mail that fails SPF/DKIM, and sends you reports.
A connected provider (Mailgun) gives you the exact records to add – see MailGun Setup. Start DMARC at p=quarantine and tighten to p=reject once you’ve watched a week of clean reports.
Send from a sub-domain (e.g. mg.yoursite.com), not your main domain. Reputation is per-sending-domain, so isolating bulk email keeps a marketing complaint from poisoning your transactional or person-to-person mail.
Never send bulk mail from a free mailbox address (@gmail.com, @outlook.com) as the From. Gmail and Yahoo’s bulk-sender rules actively reject or spam-fold this. Use an address on a domain you authenticate.
2. Warming up a new domain
A brand-new sending domain has no reputation, and mailbox providers are suspicious of a domain that suddenly sends thousands of emails on day one – that pattern looks exactly like a spammer. The fix is to ramp volume gradually so you build a track record of wanted mail.
A sensible ramp for a new domain:
| Stage | Daily volume | Send to |
|---|---|---|
| Days 1 – 3 | 50 – 100 | Your most engaged people – recent signups, known-active customers |
| Days 4 – 7 | a few hundred | Still your most engaged segment |
| Week 2 | ~1,000 | Widen to recently-active subscribers |
| Weeks 3 – 4 | double every few days | Broaden as open rates stay healthy |
| After ~30 days | full volume | Your whole active list |
The exact numbers matter less than the principle: start small, send to people most likely to open, and grow only while engagement stays good. Watch your provider’s dashboard – if complaints or bounces climb as you scale, slow down.
Warm up with your best content. During warm-up, send the emails people most want (a genuinely useful newsletter, an order confirmation) rather than a hard-sell blast – high open rates early teach mailbox providers that your mail is wanted.
The ramp is not about hitting exact numbers, it’s about building a track record. Providers watch how engaged your recipients are as volume grows. Send to your keenest people first, keep opens high and complaints near zero, and grow only while those signals stay healthy.
3. List hygiene – the ongoing part
Reputation erodes fastest from sending to people who don’t want it or addresses that don’t exist:
- Use double opt-in. Confirming each address before it joins a list keeps fake and mistyped addresses off entirely – the single most effective hygiene measure. See Double Opt-in.
- Let suppression do its job. Super Speedy Emails auto-suppresses hard bounces and spam complaints, so you stop mailing dead and hostile addresses without lifting a finger. See Bounces, Complaints & Deliverability. Don’t work around it by re-adding bounced addresses.
- Make unsubscribing easy. A visible unsubscribe link (and the one-click List-Unsubscribe header the plugin sets) means unhappy recipients leave quietly instead of hitting “spam” – a complaint hurts your reputation far more than an unsubscribe. See Unsubscribes & the Preference Centre.
- Re-engage or drop dormant subscribers. Addresses that never open for 6 – 12 months drag your engagement metrics down. Periodically send a “still want these?” email and let the non-responders go.
- Don’t buy or scrape lists. Ever. It’s the fastest way to a blocked domain, and it’s illegal in most jurisdictions.
Re-adding a bounced or complained address because “they’re a good customer” undoes the one thing keeping your reputation clean. Auto-suppression exists precisely so you stop mailing dead and hostile addresses. Leave it alone, and never import a purchased list to “get started faster”.
Watch these numbers
Your provider’s dashboard (and the plugin’s Tracking & Reporting) show the metrics that matter:
- Bounce rate – keep it low; a spike means a stale or bad-quality list.
- Complaint (spam) rate – keep it under ~0.1%. Mailbox providers start throttling you around 0.3%. Even a handful of complaints on a small send is worth investigating.
- Open rate – a floor on engagement (open tracking is imperfect), but a sudden drop often signals you’re landing in spam.
Quick checklist
- [ ] SPF, DKIM, and DMARC set up on a dedicated sending sub-domain (MailGun Setup)
- [ ] From address is on a domain you authenticate (not a free mailbox)
- [ ] New domain warmed up over ~30 days, starting with engaged recipients
- [ ] Double opt-in on for marketing lists (Double Opt-in)
- [ ] Auto-suppression left alone to clean bounces/complaints (Bounces & Complaints)
- [ ] Unsubscribe link prominent; complaint rate watched and kept under 0.1%
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