Reseller playbook · Intermediate · an afternoon

How to stop email going to spam — One Client's List Can Sink Everybody Else's Mail

On shared infrastructure you do not have a deliverability problem per client — you have one reputation, and any account on it can spend yours.

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Straight answer first

Start by establishing whether the problem belongs to the domain or to the neighbourhood: a single client with unfinished authentication is a twenty-minute fix, while a shared outbound reputation dragged down by somebody else's purchased list is a policy problem wearing a technical costume.

The afternoon this takes is mostly evidence gathering. Score the domain, compare it against a second account on the same platform, then decide whether you are repairing a record or having a conversation about acceptable use.

Written by the Hosting Seller staff · Checked 24 August 2026

Intermediate

Skill assumed

Stages of diagnosis

Free

Cover included

Tested

Tested on our own platform

This assumes you host mail for other people's businesses and that at least one of them sends more mail than they told you about. It is written for the person who gets the phone call, not the person who wrote the newsletter.

The order of the checks matters more than any individual fix. Work outward from the domain to the platform, because starting at the platform makes every client's problem yours by default.

The shared reputation you did not know you were underwriting

Outbound mail from a shared reseller account leaves by a shared route. Filtering providers score that route, which means a single client running a bought list of forty thousand addresses is spending reputation that the thirty-nine well-behaved accounts beside them depend on.

This is the failure mode worth designing against, because it does not announce itself as an incident. It arrives as several unrelated clients mentioning, in the same fortnight, that their mail seems slower to land — which is exactly the shape of a problem nobody escalates until it has cost somebody an order.

Finding the account that is doing it

Compare like with like. Run a fully authenticated domain of your own through a mail-testing service, then run the complaining client's domain through the same test. If yours scores well and theirs does not, the problem is theirs and it is almost always unfinished authentication. If both score badly on the same signals, look at the neighbourhood.

From there, look at volume rather than complaints. The account sending several thousand messages a day through hosting mail is the one to talk to, and it is rarely the account that raised the ticket. WHM's account listing plus the mail queue tells you more in five minutes than a week of guessing.

The acceptable-use conversation, and the offer that goes with it

Never open with a threat of suspension. Open with the number: this is how much mail your account sent, this is what it is doing to delivery for everyone, and here is the way to keep sending it. Bulk mail belongs on a transactional or marketing platform built for it, and moving a client onto one is a service you can charge for.

Then write the rule into your terms so the next conversation is shorter. A line separating ordinary correspondence from bulk sending, with a stated threshold, converts an awkward negotiation into a clause both sides already agreed to.

What to automate before the next one

Two things make the recurrence cheaper. First, set the mail limits on the package rather than the account, so a new client cannot become this problem before you notice. Second, put SPF and DKIM into the account build so no client on your shelf is ever the unauthenticated one.

Beyond that, the platform carries the parts that are genuinely nobody's job: spam and virus filtering on every mailbox, Imunify360 across every client site, and daily backups you can restore from without a ticket. Support answers at any hour, for you and for the client whose invoice is sitting in a junk folder.

Built for people who host other people's mail

Every guide here is tested on the reseller platform we sell: WHM over cPanel, mailboxes on the client's own domain, spam and virus filtering fitted as standard, and limits you set per account.

Support answers for your clients as well as for you, which is the difference between a deliverability question and an escalation you have to own alone.

Diagnosis ordered domain first, platform second
The noisy account found by volume, not complaint
The acceptable-use clause worth writing now
Package limits that stop the next one

Why Hosting Seller

On every plan, as standard

An order of checks, not a list of tips

Works outward from the client's domain to the shared route, so you do not adopt somebody else's problem by mistake.

The culprit found by numbers

Uses volume from the account listing and the mail queue rather than whichever client shouted first.

A script for the awkward call

Opens with the figure and an alternative, not a suspension notice — which is what keeps the account.

A clause for next time

Turns the conversation into a term both sides already agreed, with a threshold written down.

Prevention at the package

Puts mail limits and authentication into the build so a new client cannot repeat it unnoticed.

Filtering fitted as standard

Spam and virus filtering on every mailbox, and Imunify360 across every client site, without being configured.

First Steps

From choosing to live

1
Score the complaining domain against a known-good one
Run both through the same mail-testing service in the same hour. Two results on one screen tell you whether you are looking at a domain problem or a neighbourhood problem, and that fork decides everything that follows.
2
Finish authentication on the client's domain first
SPF, DKIM and DMARC all passing and aligned. Most long-running spam-folder cases on a reseller account turn out to be a client whose authentication was never completed, which is cheap to fix and easy to prove.
3
Find the volume, not the volume of complaints
Check the mail queue and the per-account counts in WHM. The account causing the trouble is usually quiet on your helpdesk, because from its own point of view everything is working perfectly.
4
Move bulk sending off hosting mail
Correspondence through the mailbox, campaigns through a platform built for campaigns. Offer to set it up and bill for it — the client keeps sending, the shared route recovers, and you have added a line to the invoice.
5
Set the limit in the package and watch it
Cap hourly sending at the package level so the next client cannot repeat this before anybody notices. Then keep an eye on the queue: a rising count is the earliest warning you get.

In the Box

Packed with every plan

Spam and virus filtering fitted to every mailbox
Mailboxes on the client's own domain, not a shared one
You set the limits each client account gets
Imunify360 on guard on every client site
Daily backups across every client account
WHM for you, a cPanel of their own for every client
A 99.9% uptime target, watched day and night
Real people answer, for you and for them
Private nameservers under your own brand
Free SSL on every client site, reissued before it lapses

Across the Counter

Things people ask us all the time

One account on my reseller plan got the shared route in trouble — how do I identify which?

By volume, not by complaint. Read the mail queue and the per-account send counts in WHM: the account responsible is usually the one that has not contacted you, because its own mail appears to be leaving perfectly happily. The complaints come from its neighbours.

Should I let clients send newsletters through hosting mail at all?

Not at any real volume. Hosting mail is built for correspondence, and campaign sending on the same route makes every other client's delivery your problem. Put a threshold in your terms, then offer the migration to a proper sending platform as paid work.

What do I tell a client whose mail is in spam because of somebody else?

Something true and short: the cause is not their configuration, you have identified it, and here is the date it will be resolved. Then finish their authentication anyway, because a fully aligned domain is the best insurance any single account has against its neighbours.

What is the uptime target, and what happens if it is missed?

99.9%, watched by monitoring day and night, and the terms give a pro-rated credit on any month that falls short through a fault at our end — ask and it is applied. We call it a target rather than a contractual SLA deliberately, because that is what it honestly is.

Moving your site to another host? Start with this checklist.

A step-by-step order of work for a move your visitors never spot: which files to copy first, how to carry email across without losing one message, the right moment to repoint DNS, and the two mistakes behind nearly every hour of downtime people ring us about.

Host other people's mail properly.

Per-account limits, filtering on every mailbox, and support that will talk to your client directly.

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