The Complete SMTP Service Guide: Which One To Use And Why

Every email you send from WordPress has to leave your website somehow. The service that carries it out into the world decides how fast it goes, how much it costs and, most of all, how often it lands in the inbox where your reader will see it.

That service is called an SMTP service, or a sending service. There are dozens of them, they all describe themselves in the same words, and their pricing pages are built to be compared with nothing. So people pick one at random, or pick the one a friend uses, and never know if it was right for them.

This guide fixes that. I will explain what a sending service does in plain words, the eight things that make one different from another, and then walk through the eight services most marketers choose between. You get real prices at four list sizes, a table that tells you which one fits your situation, and a clear picture of how the ResultsAiX Mailer works with any of them.

What A Sending Service Does

SMTP stands for Simple Mail Transfer Protocol. It is the language mail servers use to pass an email from one to the next. When you press send, your email is handed to a mail server, that server talks to the mail server of your reader’s inbox provider (Gmail, Outlook, Yahoo, Apple and the rest), and the inbox provider decides where it goes: the inbox, the promotions tab or the spam folder.

A sending service is a company whose whole business is running those outgoing mail servers well. You give it your email, it delivers it, and it reports back on what happened: delivered, opened, bounced, marked as spam.

Here is the journey of one email from your WordPress site:

Why WordPress Needs One

Out of the box, WordPress hands email to the web server it runs on. A web server is built to serve pages, not to deliver mail at scale. It has no sending reputation, it usually does not sign your email with your domain, and most hosts cap how many emails it may send in an hour.

A professional sending service gives you four things your web server cannot:

• Reputation. Mail servers that inbox providers already know and trust.
• Authentication. Every email signed for your own domain, so Gmail and Outlook can prove it really came from you.
• Speed and volume. Thousands of emails an hour, every hour, without your host stepping in.
• Feedback. Bounces, complaints and unsubscribes reported back automatically, so your list stays clean by itself.

The ResultsAiX Mailer is the brain: your list, your tags, your broadcasts, your automations and your reports, all on your own WordPress. The sending service is the engine that carries each email out. You choose the engine, and you can change it, or run several, whenever you like.

The 8 Things That Make Services Different

Every sending service delivers email. What separates them is how they do it, what they charge and how easy they are to live with. Once you understand these eight points, you can read any pricing page in two minutes and know whether it suits you.

1. Shared IPs Or A Dedicated IP

Every email leaves from an IP address, and inbox providers keep a reputation score for each one.

• Shared IP: you send from a pool of addresses the service shares between many good customers. The service manages the reputation for you, and you benefit from the pool’s history from your very first email. This is what almost everyone should start on.
• Dedicated IP: an address used only by you. Your reputation is entirely your own. It makes sense once you send steadily, at volume, every week, usually from around 100,000 emails a month. It needs a warm-up period, and most services include one on their bigger plans or sell it as an add-on.

Today your domain’s own reputation matters even more than the IP. Gmail and Outlook judge the domain in your From address, which is why authenticating your domain (SPF, DKIM and DMARC) is the single most valuable thing you can do, on any service.

2. API Or SMTP

Those are the two ways to hand an email to a service, and the ResultsAiX Mailer supports both. Its Sending tab has a built-in connection for each major service, plus a Bring-your-own SMTP connection for anything else.

3. How They Charge

There are three pricing models, and knowing which one a service uses tells you how the bill will grow.

Because the ResultsAiX Mailer holds your list, you never pay a sending service by the number of contacts. You only pay for the emails you send. A list of 50,000 people that you email once a week costs about the same as sending 200,000 emails a month.

4. Daily And Hourly Limits

Most services count your allowance per month. A few count it per day, especially on free plans, and new accounts often start with a lower daily limit that rises once the service has seen you send well. The Mailer handles every kind of limit for you: you type the number into the connection’s Daily limit box, and the queue paces itself to fit, then carries on the next day.

5. Deliverability Tools

Every good service signs your email with DKIM once you verify your domain, processes bounces, and reports spam complaints. The differences are in the extras: inbox placement tests, email validation, reputation monitoring, dedicated IP warm-up and log history. Nice to have, but your own list quality and domain authentication do far more for your inbox rate than any extra.

6. Ease Of Setup

Every service asks for the same core steps: create an account, verify your domain with a few DNS records, create a key, paste it into the Mailer. The difference is how much is in the way. Some services are ready in fifteen minutes. Amazon SES needs a region choice, a domain identity and a request for production access, which takes a day.

7. Support

When you want help, you want a human who knows email. Support ranges from ticket only, through live chat, to phone support and a named account manager on large plans. If you are not technical, good support is worth more than a few dollars a month.

8. Where Your Data Lives

Some services let you choose US or EU servers, which matters if your business or your readers are in Europe. Mailgun offers US and EU regions, and the Mailer has a Region box for it. Amazon SES runs in many regions, and you pick one. SMTP2GO has location-specific servers for the US, the EU and Australia.

The 8 Main Services, One By One

Here are the eight services marketers most often choose between. Every one of them has a built-in connection in the ResultsAiX Mailer, so whichever you pick, you paste in your key and send. For each one you will see what it is best at, who it suits and exactly what the Mailer asks for.

SMTP2GO

SMTP2GO is a sending service and nothing else, and it does that job very well. Setup is quick, the dashboard is clear, reports are easy to read, and paid plans include chat and phone support as well as tickets. It works both as an API and as an SMTP relay, verifies your domain with three simple CNAME records, and includes a dedicated IP from its Professional plan.

• Best for: anyone who wants a reliable service that is easy to live with, from a first list to a list of hundreds of thousands. It is what I use.
• Free start: 1,000 emails a month (up to 200 a day).
• The Mailer asks for: an API Key.

Amazon SES

Amazon Simple Email Service is the lowest cost way to send real volume: you pay per email with no monthly plan. It is built for developers, so the setup uses words like identity, region and sandbox, and new accounts send only to verified addresses until you request production access. The Mailer’s built-in guide and the Training tab walk you through every step, in order.

• Best for: bigger lists that send often, where the saving adds up quickly. Many people add it as a second connection once their list has grown.
• Free start: new AWS accounts receive Free Tier credits that cover SES.
• The Mailer asks for: Access Key, Secret Key and Region.

Brevo

Brevo is a full marketing platform with its own campaign editor, automation and contacts, and it can also send for you through its API. Its free plan allows 300 emails a day, and its paid plans count a monthly volume of emails.

• Best for: small lists that want to start free, and businesses that already use Brevo for other channels.
• Free start: 300 emails a day.
• The Mailer asks for: an API Key.

Mailgun

Mailgun is a developer favourite with detailed logs that show exactly what each receiving server said. It runs separate US and EU regions, encourages sending from a subdomain such as mail.yoursite.com, and includes a dedicated IP on its Scale plan.

• Best for: people who like detailed logs, and businesses that want EU data hosting.
• Free start: 100 emails a day.
• The Mailer asks for: API Key, Domain and Region (US or EU).

Postmark

Postmark is known for outstanding inbox placement and fast delivery. It keeps broadcast email in its own Broadcast message stream, separate from receipts and password resets, and it expects a clean, opted-in list. It is one of the most respected names in email delivery.

• Best for: businesses where every email arriving matters more than the cost per email.
• Free start: 100 emails a month to test with.
• The Mailer asks for: the Server Token of your Broadcast stream.

SendGrid

SendGrid, now part of Twilio, is one of the best known sending services in the world, with plans that scale into the millions and a dedicated IP included on its Pro plan.

• Best for: growing businesses that want a big, established name.
• Free start: a 60-day trial at 100 emails a day.
• The Mailer asks for: an API Key with Mail Send permission.

Resend

Resend is the newest service in this guide and one of the simplest to set up: add your domain, add a few DNS records, create a key. Its free plan includes 3,000 emails a month, and its paid plans have no daily limit.

• Best for: people who want to be sending within minutes, on a modern, clean dashboard.
• Free start: 3,000 emails a month (up to 100 a day).
• The Mailer asks for: an API Key.

Elastic Email

Elastic Email is one of the lowest cost monthly plans for larger volumes, with email verification included on its Starter plan and webhooks, sub accounts and custom rDNS on Pro. With your domain fully authenticated, it is a sound budget choice.

• Best for: large lists on a careful budget who want a monthly plan rather than pay per email.
• Free start: 3,000 emails a month (up to 100 a day).
• The Mailer asks for: an API Key.

What They Cost, Side By Side

Every price below is as published by each provider on its own pricing page, in US dollars, with monthly billing. Providers change their prices from time to time, so check their page for today’s rates before you buy. Each table names its source.

Free Plans And Trials

Prices as published by each provider; check their page for today’s rates. Sources: smtp2go.com/pricing, aws.amazon.com/ses/pricing, brevo.com/pricing, mailgun.com/pricing, postmarkapp.com/pricing, twilio.com (SendGrid Email API pricing), resend.com/pricing, elasticemail.com/email-api-pricing.

Monthly Cost At Four List Sizes

This is what each service costs for one month of sending at each volume, on the lowest plan that covers it. Remember these are emails sent, not subscribers: 10,000 emails is a list of 2,500 mailed once a week.

Prices as published by each provider on its own pricing page, monthly billing, US dollars; check their page for today’s rates. How each figure was worked out:

• Amazon SES: $0.10 per 1,000 emails. Attachments add $0.12 per GB.
• SMTP2GO: the plan for each volume on its pricing page: 10,000 ($15), 50,000 ($30), 100,000 Professional ($75, dedicated IP included), 250,000 ($170). Paying yearly gives 2 months free.
• Elastic Email: Starter for up to 50,000 ($19), 100,000 ($29) and 250,000 ($99). Pro, with webhooks, starts at $49.
• Resend: Pro 50,000 ($20), Pro 100,000 ($35), and Scale 200,000 ($160) plus 50,000 extra emails at $0.80 per 1,000 for 250,000.
• SendGrid: Essentials 50,000 ($19.95), Essentials 100,000 ($34.95), Pro 300,000 ($249) for 250,000.
• Mailgun: Basic 10,000 ($15), Foundation 50,000 ($35), Foundation 100,000 ($75), Scale 250,000 ($215).
• Postmark: Basic at 10,000 ($15), 50,000 ($55), 125,000 ($115) and 300,000 ($245), the tiers that cover each volume.
• Brevo: Starter at 10,000 ($17), 50,000 ($56) and 100,000 ($82). Above 100,000 a month, Brevo builds a larger plan for you.

Dedicated IPs

As published by each provider; check their page for today’s rates.

Which One For Which Person

Find the line that sounds most like you. If two lines fit, pick the one higher up the table: getting started well beats saving a few dollars.

The Path Most People Follow

You do not have to make one choice for life. Here is the path I see work again and again:

How The ResultsAiX Mailer Works With Them

This is where owning your email on WordPress really pays off. The Mailer is not tied to any sending service. You connect the ones you choose, decide how they share the work, and change your mind at any time without touching your list, your automations or your reports.

The Sending Tab: All Your Connections In One Place

In the Mailer, open Delivery, then Sending. The Sending Providers table lists every connection with its provider, whether it is active, its priority, how many emails it has sent today, its daily limit and its last test result. You can add as many connections as you like: any provider, and several accounts of the same provider.

Adding A Connection

Click + Add Sender, give it a Display name and choose the Provider. As soon as you pick one, the form shows a short guide for that service: what it is best for, how setup goes, how it charges, and the steps to follow in order, with a link to the full guide in the Training tab. Then fill in what that provider asks for:

Every connection then has the same Routing section: From name, From email, Reply-To, Daily limit (0 = unlimited), Priority (lower = preferred) and an Active tick box. Click Save Sender and the connection appears in the table.

Test Before You Send

Each row in the table has a Test link. It sends a test email through that one connection to your site’s admin address and shows the result straight away, then records it in the Last test column with the time. You can also send yourself a test from any broadcast before it goes out.

Priority And Automatic Failover

Give each connection a priority number. The lowest number sends first. If that connection reaches its daily limit or has a problem, the next one in line takes over automatically, so your broadcast keeps going. If a single send does not go through, the queue tries it again with a growing delay, up to three attempts.

Rotation: Share The Work Between Services

Below the providers table sits the Send Rotation & Warmup panel. Choose how your connections share the sending:

Failover always stays underneath: whichever mode picks the connection, if one has trouble the next in line delivers the email. The panel shows each connection’s sends today, its share, its capacity left and an Authentication badge that confirms your domain is set up for that provider. Tick Strict DKIM guard and only authenticated connections take part in rotation.

Warmup For A New Account

A brand new account or a new sending domain has no history yet, so the smart move is to start small and grow. Tick Warm up on a connection and choose a pace:

Then send normally. Each day the queue sends up to that day’s cap and the rest waits and continues the next day, so a 20,000-email broadcast on the Standard pace completes in about eight days. When warmup reaches the connection’s daily limit, the row shows Warmup complete.

Daily Limit And The Hourly Ceiling

Two settings keep your sending smooth and steady:

• Daily limit, on each connection. Set it to your plan’s allowance and the Mailer paces each send to fit, then picks up the next day.
• The hourly ceiling, in Setup, then Settings, under Operations: “Never send more than this many broadcast emails an hour”. One ceiling for all your broadcasts together, spread evenly across the hour. For example 900 means about 15 a minute and never more than 900 in any hour. Automation and welcome emails are never held back by it, so new subscribers always get their welcome straight away.

Next to it, Queue batch size and Queue interval (seconds) set your normal sending speed, and an optional sending window lets broadcasts go out only between the hours you choose. On my own list I send at about 2,000 an hour: fast enough to reach everyone the same day, and steady enough that every inbox provider sees a calm, regular sender.

Every broadcast can also have its own speed in emails an hour, and its report shows the progress live: how many have gone, how many are waiting, the pace and when it will finish.

Bounces And Complaints Come Back Automatically

For every API connection, the Sending tab shows a Bounce & complaint webhook URL with a Copy URL button. Paste it into your sending service’s webhook settings, tick the bounce, spam complaint and unsubscribe events, and those people are taken off future sends automatically. The Mailer treats a hard bounce (an address that does not exist) differently from a soft bounce (a full mailbox), so real people stay on your list.

Send A Broadcast Through One Connection

Each broadcast has a Send via choice. Use it to send one particular broadcast through one connection, for example your partner mailings through a separate account. If that connection reaches its limit mid-send, the others still take over, so the broadcast always completes.

Why I Start People On SMTP2GO

When someone asks me which sending service to use, my answer is SMTP2GO, and it is the one I use myself. Here is why.

Start on SMTP2GO, get your domain authenticated, build the habit of sending every week, and when your list is big enough that the bill matters, add Amazon SES as a second connection and let rotation share the load. That is a setup that serves a list of 500 or 500,000.

Your First 14 Days

Here is the order I would follow to go from no sending service to a steady weekly broadcast on your own domain.

Questions People Ask

What To Read Next

This is the second of 15 free AiX Training Guides. Guide 3 sets up SMTP2GO from start to finish, and Guide 4 shows you everything that helps your email reach the inbox.

Your First Step, Today

Work out one number tonight: your list size times the emails you send each month. Find that number in the cost table, find yourself in the Which One table, and you have your answer.

Guide 3 sets it up with you, step by step.