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Everything You Need to Know When Choosing an SMTP Service in 2023

SMTP is an abbreviation for Simple Mail Transfer Protocol, the standard protocol for exchanging emails over the Internet. This system determines how emails are delivered across the web, so it is indispensable.

At UniOne, we work to make sending emails as easy as possible, so we provide an SMTP API you can connect to and send thousands of emails per hour. We’ll explain what SMTP is, how it works, and the tips for choosing the best SMTP service.

What Is SMTP?

It is a communication protocol for transmitting electronic mail. It was founded in the 1980s when people sought to build a standard for communicating on the ARPANET network, the predecessor to the modern internet. Since then, there has been many improvements, and it has become the standard protocol for email exchange.

How Does SMTP Work?

Most people sending electronic mail don’t understand what goes on behind the scenes to ensure they get to the intended recipient. When you hit the send button, the message goes from your mail server to that of the intended recipient and finally to their inbox. Here’s a step-by-step breakdown:

  • A mail user agent (MUA) connects your mail client to the SMTP servers. This connect is known as a handshake and occurs through a port (25, 465, 587, or 2525).
  • Your client gives the message body and the sender's and recipient's email addresses to the server. 
  • A mail transfer agent checks if the sender and recipient's address share the same domain. If so, it transfers the message directly to the recipient's server. Otherwise, it consults the Domain Name System (DNS) to look for the IP address of the recipient's mail servers and sends the message there.
  • The receiving server verifies the message and passes it to the email client, where the recipient can open and read it.

The process outline above occurs in just a few seconds of hitting the send button.

Types of SMTP

The two main types are transactional and marketing.

Transactional is designed for one-on-one communication. It's built for business-related messages such as invoices, support emails, purchase confirmations, etc. Security is the primary focus here because transactional messages involve personal data and sensitive information.

Marketing is designed for sending bulk messages to a large recipient list. The primary consideration here is ensuring that your messages get to the intended recipients and aren't bounced or marked as spam.

Why Do You Need an SMTP Service Provider?

It helps you send emails reliably to users. The providers have well-configured servers that enable you to send messages with little hassles. When you choose a reputable provider, you’ll have few issues getting your emails delivered.

Things to Consider When Choosing An SMTP Service

The factors to consider to choose the best SMTP provider include:

  • Deliverability rates: This refers to the percentage of emails you send that get to their intended recipients. 95% and higher is a good deliverability rate for a provider. Anything less than 95% means a considerable number of your messages will bounce.
  • Ease of use: It should be easy to set up your email provider and navigate different features. Any platform that’s difficult to use will give you headaches and make sending messages dreadful.
  • Customer support: A good provider should offer good customer service. You should be able to talk to a human support representative if need be.
  • Security: Your platform must have advanced security features to prevent theft and abuse of sensitive information and customer data.
  • Analytics: You should be able to monitor important metrics such as open rates, bounce rates, click-through rates, etc.

Top 10 SMTP Services

  1. A platform built for high-volume senders, with features such as IP warming, email list monitoring, and transactional email templates.
  2. Brevo (formerly Sendinblue): A secure platform with an interactive user interface.
  3. SendPulse: An easy-to-use service for large volume senders. It also supports web push and SMS marketing.
  4. SendGrid: Best for sending mass email newsletters.
  5. Mailjet: A popular provider offering a free service that lets you send up to 200 emails daily.
  6. MailChimp: The world's most popular email marketing platform with a broad feature set.
  7. Mailgun: A good platform for automated marketing messages.
  8. GetResponse: Offers interactive templates to help you send appealing marketing messages.
  9. Moosend: A good solution for small businesses.
  10. Amazon SES: A cloud-based platform with advanced features, but is a bit complex to use.


We have explained what SMTP is, its types, and how it works. We also explained why you need an SMTP provider and the tips to choose the best one. Adhere to these tips, and you’ll likely choose a provider that’ll give you the best service.

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