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.
Table of Contents
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.
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.
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%
- MailGun Setup — the DNS/authentication mechanics
- Bounces, Complaints & Deliverability · Double Opt-in
- Unsubscribes & the Preference Centre · Tracking & Reporting
