Domain reputation is one of the biggest factors in cold email deliverability. This covers how to pick and configure domains for Maildoso campaigns: how many mailboxes to put on each domain, which TLDs to avoid, and how to protect your main website.

Our recommendation is 20 to 50 SMTP mailboxes per domain. Going higher is also totally okay — up to 99 SMTP mailboxes per domain; we have customers running 99 mailboxes on a single domain.

Google Workspace domains are capped at 5 mailboxes per domain regardless; see Setting up domains and mailboxes.

What actually matters: your warmup volume. The number of mailboxes on a domain is not what decides your deliverability. What's important is to keep the number of warmup emails higher than the number of cold emails. Sending limits are applied per mailbox, so follow the per-mailbox warmup and campaign numbers in What's the daily email limit per email account? no matter how many mailboxes share a domain.

One trade-off to keep in mind: a domain-level problem (a blacklist listing, a registry suspension, a DNS issue) takes every mailbox on that domain down at once. More mailboxes per domain means fewer domains to buy and manage, but a bigger share of your setup is affected by any single incident. If that matters to you, stay toward the lower end of the range or spread your mailboxes across more domains.

Yes — that's well within limits. Our recommended range is 20–50 per domain, and up to 99 is fine.

Yes, up to 99 SMTP mailboxes per domain is totally okay. Just keep your warmup volume higher than your cold email volume.

One domain is enough — 20 mailboxes is within the recommended 20–50 per domain. Use two if you'd rather spread the risk.

2–5 domains (20–50 mailboxes each). If you're planning at this scale, contact support — we can help you lay it out.

Stick to established TLDs for cold email: .com, .info, .co, and .one are all safe choices.

Avoid .online, .site, .xyz, .space, and .website — these TLDs have a track record of being suspended by their central registry when used for bulk cold email, which takes the domain (and any mailboxes on it) down with no warning.

.click and .top can be kept on a case-by-case basis rather than being recommended by default — ask support if you're specifically considering one of these. .sbs and .cfd are currently above what we consider an acceptable risk level and should be avoided.

If you already have mailboxes on a domain with a risky TLD, you don't need to panic or pause sending — but if that domain does get suspended, replacing it is the fix; see Domain replacement. If the suspension shows in your dashboard as MANUALLY DISABLED, see My domain shows "MANUALLY DISABLED" — can it be reactivated?

Before using any domain for a campaign, it's worth checking it isn't already listed on a major blacklist. Aged domains (registered and DNS-active for a while) generally have a head start on reputation compared to a domain created the same day you start sending. You don't need to manually verify this before every send — Maildoso monitors reputation on your domains — but it's good to keep in mind when choosing which domain to put where. If a domain does get flagged, see Domains flagged as blacklisted: how we help, and where refunds fit in for how we handle it.

If your primary company website domain isn't already connected to Maildoso, don't connect it for cold email — use a separate domain dedicated to campaigns instead, so a deliverability issue on a sending domain never touches your main site's reputation. If your primary domain is already connected to Maildoso and you want that separation now, see Can I stop using Maildoso's DNS or move my domain to another DNS provider? to move it back to your own DNS.