CrestlineTech provides secure, UK GDPR-compliant transactional email infrastructure and communication APIs for financial services, SaaS platforms, and enterprise software providers across the United Kingdom.
Purpose-built communication infrastructure designed to meet the exacting requirements of regulated industries and high-volume SaaS platforms.
High-throughput transactional email delivery with dedicated sending queues, real-time event tracking, and intelligent retry logic optimised for reliability.
Enterprise SMTP relay with TLS enforcement, authentication via API keys or credentials, and detailed per-connection logging for audit purposes.
RESTful API with comprehensive SDKs, webhook event streams, and sub-second response times. Full API versioning ensures backwards compatibility.
Guided SPF, DKIM, and DMARC configuration with automated record validation. Domain authentication is mandatory for all accounts before activation.
Granular delivery reporting with per-message event tracking, exportable logs, scheduled reports, and a real-time metrics dashboard.
Automated suppression list management with ISP feedback loop processing. Exceeding complaint thresholds triggers immediate automated alerts.
Dedicated sending IPs available on qualifying plans with managed IP warm-up programmes and ongoing reputation monitoring through major blacklist providers.
24/7 automated abuse detection with a dedicated compliance team reviewing flagged accounts. Policy violations result in immediate account suspension.
Centralised suppression management with automatic unsubscribe and bounce handling. Import and export via API or dashboard CSV upload.
CrestlineTech operates on a strictly permissioned basis. Our infrastructure is designed exclusively for compliant, opt-in transactional and authorised commercial communication.
All new accounts require a manual application review and identity verification. Contact our team to begin the onboarding process.
Founded in 2021 and headquartered in London, CrestlineTech Ltd provides compliant communication infrastructure to enterprise clients across the United Kingdom.
CrestlineTech was founded with a single conviction: that reliable, compliant communication infrastructure should be accessible to any legitimate business operating at scale.
We serve financial services firms, SaaS platforms, e-commerce operators, and enterprise software providers who require a communication layer that is stable, auditable, and fully compliant with UK and international regulation.
Every account on our platform has been individually reviewed and approved. We do not offer open self-serve sign-up. This deliberate approach keeps our infrastructure clean and our clients' reputations protected.
CrestlineTech Ltd
4th Floor, 12 Finsbury Square
London
EC2A 1AN
United Kingdom
Every aspect of our operations—from client onboarding to infrastructure configuration—is designed around our obligations under UK GDPR, PECR, and the broader ICO guidance framework.
No automated sign-up. Every new client application is reviewed by a member of our compliance team. We verify business identity and intended use before granting any infrastructure access.
We maintain dedicated IP pools, enforce domain authentication for all senders, and operate continuous abuse monitoring to protect the sending reputation of every client on our platform.
From transactional email to full API integration, CrestlineTech provides the reliable foundation your business needs.
Our transactional email infrastructure is purpose-built for high-volume, time-sensitive sending. Order confirmations, account notifications, password resets, and verification emails are delivered with consistent, auditable performance.
Every message is tracked through our event pipeline—delivering, bounced, opened, complained—with webhook callbacks and dashboard visibility in real time.
// Webhook event payload
{
"event": "delivered",
"messageId": "msg_01HXWYZ...",
"recipient": "user@domain.co.uk",
"timestamp": "2026-02-20T09:14:32Z",
"domain": "mail.yourcompany.co.uk",
"ip": "185.x.x.x"
}
CrestlineTech requires all client domains to be fully authenticated before any messages can be sent. SPF, DKIM, and DMARC must all be correctly configured and verified by our team.
Our onboarding engineers provide guided DNS configuration support and validate all records before your account is activated. Ongoing authentication monitoring alerts you to any configuration drift.
All plans require manual account approval and identity verification. Pricing is exclusive of UK VAT.
Manual account review · Identity verification · TLS 1.3 encryption · Abuse monitoring · UK GDPR support
Monthly subscription. All pricing exclusive of UK VAT at the prevailing rate. Invoices issued on the first of each month.
Messages beyond your plan limit are billed at £0.80 per 1,000 (Professional), £0.65 per 1,000 (Business).
Monthly rolling contracts. 30 days' written notice required to cancel. Enterprise contracts are negotiated individually.
Welcome to the CrestlineTech developer documentation. This reference covers SMTP relay configuration, the REST API, domain authentication, and compliance requirements for all clients.
CrestlineTech provides two primary integration methods: SMTP relay and the REST API. Both require valid API credentials issued during onboarding. Domain authentication (SPF, DKIM, DMARC) is a prerequisite for account activation.
Before you can begin sending, your account must have:
Configure your application's SMTP client with the following settings. All connections must use TLS; plain-text SMTP is not supported.
# SMTP Relay Settings
Host: smtp.crestlinetech.co.uk
Port: 587 (STARTTLS) or 465 (SSL/TLS)
Auth: PLAIN or LOGIN (over TLS only)
Username: your-api-key-id
Password: your-api-secret
The REST API accepts JSON payloads over HTTPS. Authenticate using Bearer token authentication with your API key.
POST https://api.crestlinetech.co.uk/v1/messages/send
Authorization: Bearer <your-api-key>
Content-Type: application/json
{
"from": {
"email": "noreply@mail.yourcompany.co.uk",
"name": "Your Company Ltd"
},
"to": [{ "email": "customer@example.com" }],
"subject": "Your order confirmation",
"html": "<p>Thank you for your order.</p>",
"tags": ["transactional", "order-confirm"]
}
All sending domains must have valid SPF, DKIM, and DMARC records before the account is activated. Our onboarding team will verify your DNS configuration as part of the approval process.
# Add to your domain's DNS (TXT record)
Host: @
Value: v=spf1 include:spf.crestlinetech.co.uk ~all
# Minimum recommended DMARC record
Host: _dmarc
Value: v=DMARC1; p=quarantine; rua=mailto:dmarc@yourcompany.co.uk
CrestlineTech is built on a compliance-first foundation. Every layer of our infrastructure—from physical security to client onboarding—is designed to meet enterprise security requirements.
We apply data minimisation principles throughout our platform. Message content is not stored beyond operational necessity. Log data is retained for 90 days by default, configurable on Enterprise plans.
We welcome enquiries from legitimate businesses. All account applications require a brief qualification call.
CrestlineTech Ltd (Company No. 13847291) is a company registered in England and Wales. Our registered office is at 4th Floor, 12 Finsbury Square, London, EC2A 1AN. We are the Data Controller in relation to personal data we collect about prospective and current clients, and a Data Processor in relation to personal data processed on behalf of our clients through our infrastructure.
We may collect and process the following categories of personal data:
We process personal data on the following lawful bases under UK GDPR:
We retain personal data only for as long as necessary to fulfil the purposes for which it was collected. Operational log data is retained for 90 days by default. Account data is retained for the duration of the client relationship and for seven years thereafter to meet our legal and regulatory obligations.
Under UK GDPR you have the right to: access your personal data; rectify inaccurate data; request erasure in certain circumstances; object to processing; data portability; and to lodge a complaint with the Information Commissioner's Office (ICO).
To exercise any of these rights, contact our Data Protection contact at dpo@crestlinetech.co.uk.
We do not transfer personal data outside the United Kingdom without a lawful mechanism in place. All primary data processing and storage occurs within the UK.
CrestlineTech Ltd, 4th Floor, 12 Finsbury Square, London, EC2A 1AN. Email: dpo@crestlinetech.co.uk. You have the right to complain to the ICO at ico.org.uk.
These Terms of Service ("Terms") govern your use of the CrestlineTech communication infrastructure platform ("Services") provided by CrestlineTech Ltd, a company registered in England and Wales (Company No. 13847291). By using our Services you agree to these Terms in full.
Access to the Services is not automatic. All applications are subject to manual review by our compliance team. We reserve the right to decline any application without providing a reason. Applicants must:
The Services may only be used for lawful communication with individuals who have provided explicit, verifiable prior consent to receive such communications. The Services must not be used for unsolicited bulk email, cold outreach to purchased lists, or any communication that would violate UK GDPR, PECR, or CAN-SPAM.
All sending domains must maintain valid SPF, DKIM, and DMARC records at all times. Failure to maintain authenticated domains may result in account suspension.
CrestlineTech targets 99.9% platform availability on a rolling 30-day basis, measured excluding scheduled maintenance. SLA credits are available on Business and Enterprise plans as described in the relevant plan documentation.
We may suspend or terminate accounts immediately and without prior notice where: a policy violation is detected or suspected; complaint or bounce rates exceed defined thresholds; our infrastructure or reputation is at risk; or we are required to do so by applicable law.
To the maximum extent permitted by law, CrestlineTech's aggregate liability for any claim arising from these Terms shall not exceed the fees paid by the client in the three months preceding the relevant event.
These Terms are governed by the laws of England and Wales. Any disputes shall be subject to the exclusive jurisdiction of the courts of England and Wales.
This Acceptable Use Policy ("AUP") sets out the conditions under which CrestlineTech Ltd permits access to its communication infrastructure. Violation of this AUP may result in immediate account suspension and potential legal action.
The CrestlineTech platform may only be used to send:
The following uses are strictly prohibited and will result in immediate account suspension:
CrestlineTech operates automated systems that monitor sending patterns, complaint rates, bounce rates, and content. Our compliance team reviews flagged accounts. We cooperate fully with law enforcement and regulatory bodies in relation to any suspected illegal use of our infrastructure.
To report suspected misuse of our infrastructure, contact abuse@crestlinetech.co.uk. Reports are reviewed within 2 hours, 24 hours a day, 7 days a week.
Sign in to your infrastructure dashboard
| Domain | SPF | DKIM | DMARC | Status | Last Verified |
|---|---|---|---|---|---|
| mail.acmesolutions.co.uk | ✓ Pass | ✓ Pass | ✓ Enforced | Active | 20 Feb 2026 |
| notify.acmesolutions.co.uk | ✓ Pass | ✓ Pass | Quarantine | Active | 18 Feb 2026 |