Need a rock-solid way to send automated emails from your app or website?
UniOne’s SMTP Relay Service makes it easy.Developed and maintained by the same expert team behind Selzy, UniOne ensures fast delivery, high inbox rates, and real-time tracking to keep your emails running smoothly, every time.
Built by the Selzy team, UniOne is purposefully designed for robust email integration that can handle millions of emails at lightning-fast speed.
It focuses on the essentials: high deliverability, real-time tracking for detailed analytics, and 24/7 support — all packed into a simple, affordable pricing model with no unnecessary extras.
Marketers and managers who need a full-featured, user-friendly email marketing platform
Developers and teams looking for a reliable, high-speed email integration via SMTP or Web API
Creating, sending, and analyzing marketing campaigns
Sending transactional and bulk emails via integration with your existing system
From $0.0015 per contact/email
From $0.0009 per email
✅ Yes
✅ Yes
✅ Yes, with automation, A/B testing, and tips
❌ No, HTTP/SMTP API only
✅ Yes, ready-to-use integrations + API-based at a speed of 1 email/sec
✅ Yes, at a speed up to 16,666 emails/sec via Web API and up to 15 emails/sec via SMTP Relay
✅ Yes
❌ No (contacts managed via usre-owned CRM/CDP/CMS)
Unlimited dashboards & visual reports, webhooks for API-based integrations
Visual stats, up to 400-day data retention, real-time logs, instant webhooks + downloadable CSV reports
✅ Yes
❌ No
Up to 5 MB
Up to 7 MB (10 MB total email size)
❌ No
✅ Yes
✅ Yes
✅ Yes
✅ Yes
✅ Yes
UniOne, built by the Selzy team, is ideal for developers and high-volume senders who need a lean, cost-effective SMTP relay or lightning-fast email API, without excessive extras.
Start for free with UniOne
Selzy is great for teams who want an all-in-one platform to build, send, and manage email campaigns — no tech skills needed.
Start for free with Selzy
Save time and money with a scalable email delivery solution.
While Selzy is a powerful email marketing tool with lots of ready-to-use features, UniOne focuses mostly on email performance at scale. Its streamlined infrastructure is optimized for blazing-fast delivery and high inbox placement, whether you’re sending 1,000 or 10 million emails per day.
Selzy offers ready-to-use integrations and supports custom connections through its Web API — UniOne takes flexibility to the next level. With SMTP relay support, UniOne can be connected to virtually any platform that supports SMTP sending.
Whether you use a popular CMS or e-commerce systems like WordPress, WooCommerce, Joomla, Drupal, Magento, and PrestaShop, running a storefront, membership site, or custom app, UniOne delivers a scalable, platform-agnostic solution built to grow with your business.
Selzy takes care of branding and visual identity inside its user-friendly interface. UniOne gives you full control. Use independent projects with their own domains, email templates, statistics and suppression lists — and send on behalf of clients or brands using a fully white-labeled SMTP relay server.
While Selzy manages email authentication under the hood, UniOne gives you granular control. With full SPF, DKIM, and DMARC support for each project’s sending domain, including custom tracking domains for link branding and assigning dedicated IP pools for different email streams, you can configure everything deeper, perfect for teams who need precise deliverability management.
With Selzy, you get beautiful campaign reports, dashboards, and timely webhooks for API-based integrations. UniOne provides real-time delivery analytics through both webhooks and event history logs, builds customizable visualizations of your email performance, and allows you to get data in CSV files, ideal for teams that want to feed data into their own systems and analyze performance at scale, without being tied to a UI.
Selzy is built for marketers — UniOne is built for developers. With flexible SMTP and REST API, clean docs, and SDKs, UniOne fits seamlessly into any stack, letting you automate transactional and bulk email delivery with minimal overhead.
Selzy ensures marketing emails are safe — UniOne is made for transactional reliability. With TLS encryption, secure credentials, and authentication, UniOne delivers secure SMTP relay services you can trust for sensitive or high-volume communications.
✅ Yes — created by the Selzy team, optimized for real-world performance
❌ Large platform with general-purpose tools
✅ Yes, but with more complexity
❌ Requires deep AWS knowledge
✅ Yes — works out of the box with WordPress, WooCommerce, Drupal, Joomla, Magento, PrestaShop & more
✅ Yes
✅ Yes
⚠️ Requires manual configuration
✅ Starts at $4/month with predictable volume pricing
❌ Tiered pricing + overages
❌ Paid add-ons for analytics, validation, etc.
❌ Complex usage-based billing
✅ Full SMTP & REST API with clean docs
✅
✅
✅
✅ Webhooks, analytics dashboard, and CSV export
✅
✅
❌ Basic logs only
✅ Custom tracking, headers, and domains
❌ Limited customization
✅
❌ No
✅ Send to your contacts from any platform
❌ Requires contact list management
⚠️ Optional storage
✅ Yes
✅ Full support with flexible setup
✅
✅
✅
✅ Yes, always included
❌ Priority support in premium plans
⚠️ Paid on higher tiers
❌ AWS ticketing only
✅ Free monthly validations included
❌ Paid add-on
⚠️ Extra cost
❌ No
✅ Yes
⚠️ Mostly US-based
⚠️ Limited regional data options
⚠️ Depends on AWS region
UniOne is the fast, flexible way to power your emails at scale — but don’t just take our word for it.
See what developers, marketers, and tech teams say about our SMTP relay service and why they made the switch 👉
“A true gem we discovered in a huge pile of email marketing software. Way more affordable than those big known brands, and it outperforms them! All we need for full blown email marketing campaigns.”
“The overview dashboard is something I really love, because of how easy it is to understand and the summary statistics of my overall opens, clicks and unsubscribe. The support desk is really great and quick to respond.”
“I sent the first (test) campaign in less than 5 minutes. How did Selzy get me? Pleasant dashboard, clear statistics, including the deliverability of emails from the campaign, send an email to contacts who haven't opened the message (with one click), simple import of contacts”
“Great buy! The builder covers everything, I was looking at the large array of design templates. The UX/UI is just smooth. Selzy makes Mailchimp look pale in comparison.”
“The best thing about Selzy is its ability to manage marketing emails with fantastic templates, simplifying the process.”
“Not kidding. Selzy is really good. their support is beyond excellent. Response time is less than 5 minutes. They staff is skilled. The ux/ui is amazing. I highly recommend everyone to use it. This company really knows what they are doing! In fact, this is one of the best LTD's I've bought in a while.”
“Selzy is cost effective to the max and it makes it clear how my list health is going. Also top of the line support. We are talking minutes no matter what time I pinged the chat.”
“I have been extremely satisfied with Selzy and would highly recommend it to anyone looking for a reliable and user-friendly email campaign management tool. The analytics and reporting tools are top-notch, providing detailed insights into the performance of my campaigns.”
“Great UI, super easy to use and navigate around. I really love the ease of use and the amazing and attractive templates it has that makes it so simple.”
“Create email campaigns super fast, and having my email list on different categories is awesome. Been using Selzy a lot, no complaints at all.”
“Instead of opting for larger platforms like Mailchimp or Constant Contact, which offer an abundance of unnecessary features and complex interfaces, I desired a more straightforward solution focused on email sending. After comparing various email marketing platforms like Sender, Sendpulse, and Mailerlite, I ultimately chose Selzy.”
“I can run a campaign easily. It’s an alternative solution to the CRM+Email marketing tool I use on a daily basis.”
“UniOne was built for performance. I’ve designed it to handle millions of emails per day with a lightning-fast API and SMTP relay, no contact storage, and full white-label support. My team will help you get everything set up — from domain authentication with SPF, DKIM, and DMARC to custom unsubscribe handling and webhook-based analytics — so your system runs clean, fast, and fully in your control.”
“Email should be fast, flexible, and developer-friendly. That’s exactly what we designed UniOne to be. Whether you’re a startup or sending millions daily, I am here to help you scale with confidence, bringing maximum value for your growth and success, and with no surprises on your bill.”
UniOne delivers over 1 billion emails every year for 1,000+ teams and platforms, with a proven 99%+ deliverability rate you can count on.
The highest standards of data protection aren’t just words for us — with secure infrastructure, encrypted connections, and strict privacy policies, every email you send and each recipient is totally safe.
UniOne is GDPR-compliant by design, giving you and your users peace of mind with every send.
Includes: domain authentication setup (SPF, DKIM, DMARC), IP warm-up guidance, 24/7 developer onboarding support, and custom domain tracking setup to boost deliverability and sender trust.
* for the first 4 months
Includes: 24/7 priority support in a group chat, onboarding assistance, deliverability consultations, and guidance on authentication and compliance.
Includes: up to 6,000 emails/month for just $4, scalable volume-based pricing, real-time analytics, and full access to SMTP & API.
Includes: private IP allocation, IP warming strategy, and ongoing delivery performance monitoring.
Includes: 6,000 FREE validations/month, bounce prevention, and sender reputation protection with optional add-on packages.
Extra validations: $2 / 1,000 emails
What is an SMTP relay service and how does UniOne support it?
An SMTP relay service helps you send transactional and bulk emails through a third-party server so they land in inboxes quickly and reliably, without managing your own infrastructure. UniOne is a fast, secure SMTP relay provider built for high-volume, time-sensitive messages. It handles the heavy lifting — authentication, deliverability, tracking, and queue management, so your emails go out smoothly every time.
Can I integrate UniOne with my own software?
Yes, easily! UniOne is designed for developers and platforms that need seamless integration. Сonnect it to your app, CRM, CMS, or website via SMTP relay or a powerful email sending API. Whether you’re using WordPress, Magento, or a custom-built tool, UniOne fits right in, handling email delivery, tracking, and reporting without disrupting your stack.
What security protocols and standards does UniOne support?
UniOne takes security seriously. With TLS encryption for secure connections, SPF, DKIM, and DMARC for your sending domain protection from spoofing and phishing, you can stay calm about your email campaigns safety. As a modern SMTP relay service provider, UniOne also complies with GDPR and follows industry best practices to keep your email data safe, authenticated, and fully traceable.
Does UniOne provide an API for automated email sending?
Yes! In addition to SMTP relay services, UniOne offers a developer-friendly REST API that lets you send emails automatically at a speed of up to 60 million messages per hour, track events in real time, and manage templates and webhooks. It’s perfect for transactional emails, real-time notifications, and any system where automation and deliverability are critical.