7 Best SMTP Relay Services for Reliable Email Delivery

SMTP relay is the process of transmitting emails from a sender's email server to a recipient's email server via an intermediary server. This ensures that emails are correctly routed and delivered to the intended inbox. SMTP relay services are third-party platforms that specialize in managing this process efficiently. They provide infrastructure, tools, and expertise to handle large-scale email delivery. These services are important because they optimize deliverability, help businesses avoid spam filters, and protect sender reputation by managing compliance with anti-spam regulations.

Choosing the right SMTP relay service can make a significant difference in email performance, engagement, and customer satisfaction. This guide explores leading SMTP relay services available, highlighting their features, pros, and ideal use cases to help you find the perfect solution for your email needs.

Here is our list of our top SMTP relay services:

MailerSend Built to deliver transactional emails quickly, securely, and reliably.
EmailSuccess Designed specifically for enterprise-level businesses and high-volume email senders.
Inboxroad An SMTP relay service that simplifies email delivery for businesses of all sizes.
Flowmailer Designed for businesses that require reliable, scalable, and secure email delivery.
SMTP.com A prominent cloud-based SMTP relay provider specializing in managing outgoing emails for high-volume senders.
Brevo A leading email marketing platform that provides reliable SMTP relay services.
Postmatery A specialized email technology consultancy that complements SMTP relay services

Our methodology for selecting the best SMTP relay services:

In selecting our top SMTP relay services, a combination of factors were considered to provide a well-rounded list:

Email Deliverability and Reputation: We favored providers with strong IP reputation management, proper DNS configurations, and consistent monitoring of blacklisting.
Authentication and Security Features: We considered services that support important email authentication protocols like SPF, DKIM, and DMARC to protect against spoofing and phishing attacks.
Support and Customer Service: We examined the quality of customer support, considering factors such as 24/7 availability, various communication channels (live chat, phone, email), and helpful resources like knowledge bases and tutorials.
Pricing and Plans: We looked for providers offering scalable solutions that can grow with your needs, without hidden fees or email volume restrictions.
User Reviews and Testimonials: We researched online reviews, testimonials, and case studies to gauge the quality and reliability of the service. Platforms like Trustpilot or G2 can provide insight into customer satisfaction.

The Best SMTP Relay Services

1. MailerSend

MailerSend is an SMTP relay service designed to handle transactional emails with speed, security, and reliability. It offers an intuitive setup, dynamic templates, and seamless integrations with platforms like WordPress, Zapier, and Firebase.

Key Features:

Robust and Secure Infrastructure: Built with SPF, DKIM, and DMARC protocols and Dedicated IP allowlists to secure sending domains and maintain sender reputation.
Scalable SMTP Relay Service: Handles transactional emails quickly and efficiently, with scalability to send millions of emails as needed.
User-Friendly Setup and Interface: Easy to set up with SMTP server credentials and intuitive dashboard for managing domains, users, and settings across multiple brands or clients.
Enhanced Email Deliverability: Proactive sender reputation management and optimized infrastructure with clean IP addresses and domain authentication to maximize inbox placement.
Dynamic Tools for Engagement and Tracking; Drag-and-drop email template builder, custom HTML editor, A/B testing, real-time analytics, and rich-text email editor for professional designs.

Built on a powerful infrastructure, it provides businesses with SPF, DKIM, and DMARC protocols to safeguard domains and maintain sender reputation. MailerSend is an excellent choice for scaling email operations.

Why do we recommend it?

Its robust security protocols, scalable infrastructure, and user-friendly interface make it ideal for businesses seeking reliable and efficient email delivery. Tools like A/B testing, dynamic templates, and real-time analytics, MailerSend helps businesses refine their communication and improve customer engagement.

Who is it recommended for?

MailerSend is an excellent SMTP relay service for businesses prioritizing transactional emails, such as e-commerce platforms, SaaS companies, and startups. Whether you’re a small business looking for an affordable yet powerful email solution or a growing company needing scalable transactional email capabilities, MailerSend delivers exceptional value and performance.

Pros:

Generous Free Plan: Offers 3,000 emails per month, suitable for small businesses or startups.
Ease of Use: The intuitive dashboard and drag-and-drop email builder simplify email creation and domain management, enabling non-technical users to operate seamlessly.
Exceptional Deliverability: With clean IP addresses, domain authentication, and active sender reputation management, MailerSend ensures that emails reliably reach recipients’ inboxes.
Powerful Analytics: MailerSend’s real-time tracking and reporting provide insights into key metrics like open rates, click-through rates, and unsubscribes.
Scalability: Its infrastructure is built for high-volume transactional emails, making it a reliable partner for scaling operations as your email needs increase.

Cons:

Limited Marketing Features: Primarily designed for transactional emails, with fewer bulk marketing tools.
Feature Restrictions on Free Plan: Some advanced features require paid upgrades.

2. EmailSuccess

EmailSuccess is a premier SMTP relay service designed specifically for enterprise-level businesses and high-volume email senders. With over 15 years of expertise in email delivery solutions, EmailSuccess provides a powerful on-premises email gateway application that ensures exceptional deliverability, scalability, and security. It is tailored to meet the demanding needs of organizations that require robust email infrastructure to manage outbound email delivery, build sender reputation, and comply with evolving authentication standards.

Key Features:

Adaptive Email Deliverability: Dynamically adjusts SMTP settings based on ISP requirements, and includes features like IP warm up and blacklist monitoring for reputation management.
Enterprise-Level Performance: Advanced queuing technology and multiple IP pools allow high-volume email handling with prioritized delivery and connection pooling for faster performance.
Advanced Intelligence: Provides detailed performance analytics, customizable log files, and integration with CMS systems for seamless data feedback.
Powerful Authentication: Ensures compliance with DKIM, SPF, and DMARC protocols for safeguarding sender reputation with robust encryption and authentication measures.
Bounce Processing: Offers detailed bounce categorization, feedback loop handling, and reporting optimizing campaign performance and minimize wasted sends.
Seamless Integration: Supports SMTP and APIs for easy integration with existing applications, along with input scripting and filtering for enhanced routing and control.

Why do we recommend it?

EmailSuccess is highly recommended for enterprise-level businesses or high-volume senders who require robust deliverability, extensive analytics, and fine-grained control over their email infrastructure. Its powerful features, including automated tuning, detailed bounce processing, and compliance with authentication standards, make it a reliable choice for managing outbound email delivery at scale.

Who is it recommended for?

Organizations with dedicated IT teams and advanced email needs will find EmailSuccess particularly beneficial for optimizing performance and maintaining security.

Pros:

High Deliverability: With advanced tools for reputation management, automated tuning, and compliance with email protocols, EmailSuccess ensures emails consistently reach the intended inbox.
Scalability: Supports high-speed, high-volume sending, making it ideal for businesses with significant email traffic requirements.
Detailed Analytics: Offers in-depth reporting on deliverability, bounce rates, and feedback loops, enabling users to fine-tune their campaigns effectively.
Integration Flexibility: Works seamlessly with existing systems through SMTP, APIs, and external filtering tools, allowing quick deployment and adaptability.
Enterprise-Level Security: Features robust encryption, dedicated IP pools, and traffic segregation, making it suitable for organizations with strict security requirements.

Cons:

On-Premises Solution: Unlike cloud-based SMTP services, EmailSuccess requires on-premises installation, which might not suit businesses seeking fully managed solutions.
Complex Setup for Beginners: While designed for enterprise users, smaller businesses or those without IT expertise might find the setup and management a bit challenging.

3. Inboxroad

Inboxroad is a dedicated SMTP relay service focused on simplifying email delivery for businesses of all sizes. With a strong emphasis on deliverability, reliability, and expert support, Inboxroad ensures that transactional and marketing emails reach recipients' inboxes efficiently. Tailored for businesses seeking an easy-to-use, scalable, and effective email solution, Inboxroad bridges the gap between technical complexity and user-friendly functionality.

Key Features:

Simplified Analytics: Inboxroad provides an intuitive dashboard that tracks crucial email metrics like bounce rates and spam complaints.
Dedicated and Shared IP Options: Offers dedicated IP options for high-volume senders, and shared IP for businesses with smaller email volumes (<250K), where reputation is collectively influenced by the pool of senders.
Personal Weekly Reports: Weekly reports provide valuable insights into email performance over time. Businesses can track trends, analyze performance, and implement strategies to enhance deliverability.
Scalable SMTP Service: Inboxroad’s infrastructure supports sending anywhere from 1,000 to 10 million emails monthly.
Exceptional Support: Inboxroad boasts an average support response time of 45 seconds, ensuring users get quick assistance when needed.

Why do we recommend it?

Its focus on providing both dedicated and shared IP options ensures that companies of all sizes can find a solution tailored to their needs. It comes with an intuitive dashboard and weekly performance insights which businesses can use to track crucial metrics like bounce rates and spam complaints. The scalable infrastructure ensures that companies can start small and grow their email operations seamlessly, sending anywhere from 1,000 to 10 million emails monthly.

Who is it recommended for?

High-volume senders, such as e-commerce platforms, SaaS companies, and marketing agencies, will benefit from its dedicated IP options, ensuring control over sender reputation and reducing deliverability risks. Smaller businesses with moderate email needs can take advantage of shared IPs for cost-effective and dependable email sending.

Pros:

Proven Results: The platform handles over 340 million emails monthly for 267+ companies, with an impressive average G2 Crowd rating of 4.8/5.
Optimized Deliverability: Inboxroad leverages advanced tools and expert monitoring to maximize inbox placement.
User-Friendly Integration: SMTP and API access ensure a quick and straightforward setup process.
Custom Solutions: With dedicated IPs and personalized reputation management, businesses have the flexibility to tailor the service to their unique needs.

Cons:

Cost Considerations: The availability of dedicated IPs and premium support may come at a higher cost compared to more basic SMTP services.
Limited Advanced Features: While reliable, Inboxroad may lack some advanced automation and analytics tools found in more robust platforms.

4. Flowmailer

Flowmailer is an SMTP relay platform designed for businesses that need reliable, scalable, and secure email delivery. Specializing in transactional emails such as receipts, account confirmations, and notifications, Flowmailer ensures seamless email communication with customers while maintaining high deliverability rates and compliance standards. A recent announcement confirms that Flowmailer, Spotler, and Tripolis are merging to form Spotler.

Key Features:

Transactional Email Optimization: Flowmailer is built to handle mission-critical transactional emails with precision.
Customizable Email Templates: The platform offers advanced template customization options for businesses to create visually appealing and responsive emails tailored to their brand identity.
Deliverability Insights: With detailed analytics and reporting, Flowmailer helps users monitor email performance, including open rates, click-through rates, and bounce rates, enabling continuous optimization.
Event-Based Messaging: Flowmailer supports event-triggered emails, enabling real-time customer engagement based on specific actions or milestones, such as purchase confirmations or password resets.
API and SMTP Integration: Easy integration with existing systems is possible through robust API endpoints and seamless SMTP relay services.

Why do we recommend it?

We recommend Flowmailer for businesses looking for a reliable, scalable SMTP relay service that emphasizes ease of use, advanced deliverability features, and high security standards. Flowmailer's cloud-based platform is designed to handle large volumes of transactional and marketing emails. Flowmailer offers analytics, real-time tracking, and automated optimization. Flowmailer's user-friendly interface and excellent customer support make it accessible for both small businesses and larger enterprises.

Who is it recommended for?

Flowmailer is best suited for companies that need a seamless and efficient email delivery service without the complexities of managing their own infrastructure. Consider Flowmailer if your organizations require scalability and flexibility, whether sending hundreds or millions of emails.

Pros:

High Deliverability: Flowmailer focuses on ensuring that emails land in inboxes, reducing the chances of being marked as spam.
User-Friendly Interface: Intuitive tools for template creation, reporting, and configuration make it accessible to non-technical users.
Regulatory Compliance: GDPR compliance and strong data encryption provide peace of mind for businesses operating in regulated industries.
Scalable for High Volumes: Flowmailer can handle a wide range of email volumes, from small-scale businesses to large enterprises.
Actionable Analytics: Advanced reporting tools give users insights to fine-tune their email strategies effectively.

Cons:

Focus on Transactional Emails: While exceptional for transactional emails, its features for bulk marketing emails may not be as robust as those offered by specialized marketing platforms.
Pricing Transparency: Pricing details may require direct contact with the company, which can be inconvenient for smaller businesses.

5. SMTP.com

SMTP.com is a cloud SMTP service provider founded in 1998 that specializes in handling outgoing emails for high-volume senders. It operates its own redundant data center in the US, and offers a range of services including tracking and reporting, reputation management, statistical analysis, and expert support. The service also provides tools for verifying a domain's DKIM records in DNS and checking forward-confirmed reverse DNS. SMTP.com requires that emails be generated locally from an internally maintained email list.

Key Features:

Email Relay API: SMTP.com offers an easy-to-use API for email relay. This enables businesses to send large volumes of emails through a reliable SMTP server.
Scalable Infrastructure: SMTP.com can handle changing email delivery demands, from small volumes to billions of emails per month, without compromising performance.
High Deliverability Rates: SMTP.com’s established reputation ensures that emails are delivered reliably, with high success rates.
Transactional Email: SMTP.com specializes in sending high-volume transactional emails such as order confirmations, password resets, and notifications.
Managed Delivery: SMTP.com ensures reliable email delivery with its scalable infrastructure that adapts to fast delivery speed requirements.
Turnkey Migration: SMTP.com offers migration assistance to help businesses transition smoothly from other SMTP service providers.
Custom API Integrations: SMTP.com offers expert help with custom API integrations for smooth email delivery setups tailored to business needs.

Why do we recommend it?

With over two decades of experience, SMTP.com offers unmatched deliverability rates and robust infrastructure that ensures emails reach their intended recipients efficiently. Based on publicly available information, SMTP.com's platform is capable of handling billions of emails per month while maintaining speed and performance.

Who is it recommended for?

Consider SMTP.com if you run a business that requires reliable, high-volume email delivery with a strong emphasis on deliverability and scalability. It’s definitely a great tool for large-scale enterprises, e-commerce platforms, SaaS providers, and businesses that rely on transactional emails like order confirmations, password resets, or notifications.

SMTP.com is also a strong fit for organizations that are transitioning from other email service providers, as it offers turnkey migration services to make the process effortless.

Pros:

Expert Support: The support team is knowledgeable and offers specialized help for any email delivery issues or integration challenges.
Managed Onboarding: The onboarding process is straightforward and well-supported by a dedicated account management team, making it easier for businesses to get started.
SMTP for Developers: Designed with developers in mind, SMTP.com provides a robust and flexible SMTP service for integration with applications, websites, and systems.
SMTP for Marketers: The platform offers tools that help marketers send and manage email campaigns, track performance, and optimize for better results.

Cons:

Primarily Focused on High-Volume Senders: While the platform is excellent for large-scale email campaigns, it may not be the most cost-effective option for small businesses or low-volume senders.
Premium Pricing: SMTP.com is a premium service, which might not be the most cost-efficient option for businesses just starting with email marketing or transactional emails.

6. Brevo

Brevo is a prominent email marketing and communication platform that offers robust SMTP relay services. Designed to help businesses send transactional and marketing emails, Brevo provides an efficient, reliable, and scalable solution for email delivery. Its user-friendly interface and advanced features make it an attractive choice for businesses looking to streamline their email infrastructure and enhance deliverability.

Key Features:

SMTP Email Delivery: Brevo offers reliable and secure SMTP email delivery for both transactional and marketing emails.
Efficient SMTP Relay: Simple integration with any application or email client to send emails using Brevo’s SMTP credentials, ensuring fast and reliable delivery.
Transactional and Marketing Emails: Supports the delivery of transactional emails like order confirmations and password resets, alongside marketing campaigns for promotions and newsletters.
Dedicated and Shared IP Options: Offers shared IP pools for cost-effective email sending and dedicated IPs for businesses that require more control over their sender reputation.
Advanced Analytics and Reporting: Brevo provides comprehensive tracking and analytics, including open rates, click-through rates, bounces, unsubscribes, and more.

Why do we recommend it?

Brevo offers a pay per usage pricing model, superb customer service in multiple languages, and provides dedicated support for higher-tier plans. Based on our assessment, even non-technical users can set up and manage email campaigns without hassle through its user-friendly interface, simple onboarding process, and drag-and-drop editors.

Who is it recommended for?

Brevo is ideal for small to medium-sized businesses looking for an all-in-one solution for email marketing and transactional email delivery. Its affordability, ease of use, and scalability make it suitable for startups, e-commerce stores, and marketing teams focused on growing their audience and improving email engagement.

Pros:

Ease of Use: Brevo’s intuitive dashboard simplifies SMTP configuration and email campaign management.
Cost-Effective: Offers competitive pricing, especially for small and medium-sized businesses.
Support for Multiple Channels: Beyond email, Brevo supports SMS marketing, chat, and marketing automation.
High Deliverability: Authentication tools and analytics enhance email performance and reputation.

Cons:

Complexity for Beginners: New users or small businesses with limited technical expertise may find the variety of features and options overwhelming at first.
Pricing Structure: Brevo’s pricing may not be the most cost-effective option for very small businesses or those with low email volumes.

7. Postmastery

Postmastery is not an SMTP relay service in itself. Instead, it is a specialized consultancy and technology provider that focuses on optimizing email delivery infrastructure, particularly for high-volume email senders. Postmastery helps businesses maximize their email deliverability and performance by offering services and tools that work with existing SMTP relay systems. In other words, Postmastery complements SMTP relay services to ensure emails are delivered efficiently and reliably.

Key Features:

Email Delivery Assessments: Comprehensive evaluations of email infrastructure to identify issues such as high bounce rates, spam filtering, or deferrals.
Postmastery Console: A unified platform offering advanced analytics and actionable insights into email delivery performance.
Outsourced Deliverability Management: Dedicated deliverability engineering services for monitoring and managing email delivery on behalf of clients.
MTA Support: Expertise in configuring and optimizing popular Mail Transfer Agents (MTAs), such as PowerMTA, Postfix, GreenArrow, Halon, and KumoMTA.

Why do we recommend it?

We recommend Postmastery for organizations that want to optimize their email delivery performance and sender reputation. With its expert-led assessments, advanced analytics through the Postmastery Console, and outsourced deliverability management, Postmastery provides a comprehensive solution for identifying and resolving email delivery challenges. Its support for leading MTAs like PowerMTA and Postfix further enhances its appeal for businesses managing large-scale email operations.

Who is it recommended for?

Postmastery is best suited for enterprises and email service providers (ESPs) with their own MTAs, businesses sending high volumes of transactional or marketing emails, and organizations that need advanced analytics and consulting to improve email deliverability and performance.

Pros:

Expertise in Deliverability: The team’s hands-on support at the infrastructure level ensures businesses achieve better email deliverability and sender reputation.
Advanced Analytics: The Postmastery Console provides in-depth data and actionable insights that empower businesses to make smarter email delivery decisions.
Outsourced Management: Allows businesses to delegate delivery monitoring and management to enable them to focus on core activities.

Cons:

Not an SMTP Relay Service: Postmastery does not handle the actual sending of emails; businesses need a separate SMTP relay service or their own MTA.
Enterprise-Oriented: Small businesses or low-volume senders may find the services and tools too complex or unnecessary for their needs.