The 10 golden rules of cold email deliverability
If you only remember ten things, make it these. Every number is the one Emelia's support gives, and every rule comes from real cases of damaged mailboxes or domains.
1. Prospect from a dedicated domain
Never from your main domain: if its reputation drops, your quotes, invoices and client emails are the ones that land in spam. Buy variants close to your name instead (get-acme.com, acme-group.com…) and redirect them to your real website.
Avoid subdomains, which don't protect the main domain, and personal Gmail addresses, which give you no domain of your own. If your company already uses Google Workspace or Microsoft 365, ideally use a separate tenant for outreach.
2. Three mailboxes per domain, five at most
Spam reports add up on the domain, not on the mailbox. Stacking 20 addresses on one domain puts all the risk in the same place, and some providers cap sending per domain. To scale up, add domains, not mailboxes.
Sizing rule of thumb: about 5,000 sends a month call for 5 to 10 mailboxes.
3. Mailboxes on Google Workspace or Microsoft 365
Emelia sends through your provider's servers: its reputation becomes yours. Google Workspace and Microsoft 365 are the benchmarks. OVH is still decent and cheap to get started. Shared hosting providers (o2switch, Infomaniak, Hostinger, Gandi, IONOS…) enforce tight quotas, degrade the IPs of accounts that prospect and often end up switching warm-up off.
Read: My emails land in spam→4. SPF, DKIM and DMARC in place, plus a tracking domain
- All three records are set at your provider, never in Emelia.
- DMARC on
p=none, never onp=reject: a strict policy gets emails rejected and can switch warm-up off. - A custom tracking domain (CNAME
trackingtoemelia.link.): it clearly improves deliverability to Gmail and Outlook.
5. Two to three weeks of warm-up, then keep it running
A new mailbox needs 2 to 3 weeks of warm-up before its first campaign, 10 to 15 days at the very least, even if the score shows 100% after a few days: score and age are two different things. You can send from a score of 80, ideally above 90.
Start gently, around 20 new contacts a day on the first campaigns, then work up to the reference setting. And keep warm-up on during your campaigns: it maintains a balanced flow of email.
6. 35 new contacts and 100 emails per day per mailbox, at most
- 100 emails in total, follow-ups included. If warm-up stays on, set the campaign to 25 new contacts and 75 emails: warm-up uses about 25 sends a day.
- Maximum emails per day must stay strictly above New contacts / day (email), otherwise follow-ups stop going out.
- About 20 emails per hour per mailbox: pick a wide window, for example 8:30 am to 5:30 pm. Emelia spreads sends across it.
- Emelia imposes no technical limit: your provider is the one that penalises. We never recommend more than 100 emails per day per mailbox.
7. One mailbox, one campaign
Limits are set in each campaign and add up on the mailbox: a mailbox used in two campaigns at 100 sends 200 emails a day. Keep one campaign per mailbox, two at most with different hours (one in the morning, one in the afternoon).
Sends far below your setting, "Mail Delivery Subsystem" returns, a wave of bounces mentioning a limit: your provider is refusing. See false bounces.
8. Fresh, verified data: under 5% bounces
- Under 5% bounces is normal, around 3% is ideal. Above 10%, stop the campaign and change your source.
- A database loses about 20% of its validity in six months: prefer a recent extraction to an old file.
- Emails found by Emelia are already verified. A list from elsewhere goes through the verifier before sending.
- Never build addresses by hand (firstname.lastname@…) and don't buy lists.
9. Two or three contacts per company, business addresses
Emailing one company in bulk triggers its security: sometimes no bounces at all, just 0% or 100% opens. Stick to two or three contacts per company and shuffle the list. Avoid consumer addresses (Gmail, Hotmail, Orange, Wanadoo): you need business addresses to write to business addresses.
10. A short message, no attachment, in the recipient's language
- No attachments: link to an online document instead.
- Zero or one image, very few links, all https, never a URL shortener.
- A plain-text signature, a real sender name, no HTML editor.
- Spintax as soon as you send lots of identical emails.
- An unsubscribe link, from the second step at the latest.
- Never all your prospects in blind copy.
The numbers to keep handy
| Setting | Recommended value |
|---|---|
| Mailboxes per domain | 3 (5 at most) |
| Warm-up for a new mailbox | 2 to 3 weeks (10 to 15 days minimum) |
| Warm-up score to start sending | 80 minimum, ideally above 90 |
| New contacts per day per mailbox | 35, or 25 if warm-up stays on |
| Emails per day per mailbox, follow-ups included | 100, or 75 if warm-up stays on |
| Pace | about 20 emails per hour per mailbox, over a wide window |
| Campaigns per mailbox | 1 (2 at most, at different hours) |
| Contacts per company | 2 to 3 |
| Bounce rate | under 5%; stop above 10% |
| Open rate | above 70% excellent, 50% fine, under 30% a problem |
| DMARC | p=none |
| Images and attachments | 0 or 1 image, no attachments |
And two monitoring habits
- Never resend to an address that bounced, not even a soft bounce: the contact leaves the sequence automatically, leave it out.
- Measure: keep open tracking on for your first campaigns, with a tracking domain. It's your only reliable thermometer.
Other cases
Frequently asked questions
The questions we get asked on this topic, answered briefly.
My provider allows more mailboxes per domain. Why stick to 3?
Because reputation is built and lost at domain level. The more mailboxes prospect from one domain, the more reports pile up on it, and the faster a per-domain quota is reached. Two domains with three mailboxes each are far sturdier than one domain with six. Emelia allows up to 5 mailboxes per domain, but we recommend sticking to 3.
Can I go above 100 emails a day if my provider allows it?
Emelia won't stop you, but we never recommend it. To send more, add mailboxes on other domains: it's safer and just as fast.
How many mailboxes do I need to send 5,000 emails a month?
Plan 5 to 10 mailboxes, spread over several domains, with 3 mailboxes per domain.
Should I keep warm-up on during my campaigns?
Yes, that's what we recommend. Then set the campaign to 25 new contacts and 75 emails per day per mailbox, to leave room for the warm-up emails.
Do my sending domains need a website?
It's not required, but redirect them to your real website: a domain showing the provider's default page hurts your credibility with curious prospects.