Documentation/Languages/Ruby

Email testing with Ruby

No gem yet, and none needed: the API is six endpoints and Ruby ships net/http. Copy the helper below into spec/support and you are done.

Before you begin

A MailFlat account
Free to start, no card. Every plan can open inboxes from the API.
An account API key
Agents → API keys in the dashboard. It looks like mf_live_… and goes in the X-API-Key header. Tick Read messages and Create and delete inboxes (inbox:read + inbox:manage): a new key can only read, so opening an inbox fails with 403 until you add the second one. Keep it in an environment variable, never in the repo. See API keys and authentication.
Ruby 3.0+ (standard library only)
That is the whole toolchain requirement.

The client

There is no Ruby package yet, and you do not need one: the API is six endpoints. Paste this helper into your test support directory and every example below works.

Ruby

# Nothing to install: Ruby ships net/http and json.
# Drop this helper in spec/support/mailflat.rb and require it.
 
require "net/http"
require "json"
require "uri"
 
module MailFlat
  API = "https://mailflat.net/api/v1"
  KEY = ENV.fetch("MAILFLAT_API_KEY")
 
  def self.call(klass, path, body = nil)
    uri = URI("#{API}#{path}")
    req = klass.new(uri)
    req["X-API-Key"] = KEY
    if body
      req["Content-Type"] = "application/json"
      req.body = JSON.dump(body)
    end
    res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
    JSON.parse(res.body)
  end
end

Your first inbox and one-time code

The whole loop: open an address, let your app mail it, read the code back, clean up.

Ruby

# 1. a real, deliverable address
created = MailFlat.call(Net::HTTP::Post, "/inboxes",
                        { prefix: "signup", retention_hours: 2 })
address = created["address"]        # signup@a7f2c.mailflat.net
 
# 2. your app sends the code to that address
MyApp.register(email: address)
 
# 3. read it back, no mocking anywhere
otp = MailFlat.wait_for_otp(address)
puts otp                            # "482913"
 
# 4. done with it
MailFlat.call(Net::HTTP::Delete, "/inboxes/#{address}")

Line by linewhat each step of this Ruby example does

create(...): Returns immediately with a real, deliverable address. Nothing is queued or simulated.
retention_hours: Optional. Messages purge themselves after it, so a skipped teardown never leaks.
wait_for_otp: Polls for you and fails loudly on timeout, instead of returning nothing three lines before the real error.
delete(): Optional but tidy. Retention would clean up anyway.

The address is real

Mail actually travels: SMTP, DKIM, the lot. Nothing is stubbed, so a broken template or a misconfigured sender fails here exactly like it would in production.

Waiting for the code

We extract the one-time code server-side and hand it to you as a field, so you never write a regex against an email body.

Ruby

module MailFlat
  # Poll /latest until the server has extracted a code, then fail loudly.
  def self.wait_for_otp(address, timeout: 60, interval: 3)
    deadline = Time.now + timeout
    while Time.now < deadline
      res = call(Net::HTTP::Get, "/inboxes/#{address}/latest")
      raise res["note"] if res["encrypted"]     # E2E inbox: server cannot read it
      otp = res.dig("email", "otp_code")
      return otp if otp
      sleep interval
    end
    raise "no OTP arrived for #{address} within #{timeout}s"
  end
end

Always set a timeout

A poll loop without a deadline turns a missing email into a hung job. Fail loudly instead: the error message should name the address you were waiting on.

Reading every message

Ruby

res = MailFlat.call(Net::HTTP::Get, "/inboxes/#{address}/messages")
 
res["emails"].each do |msg|           # newest first
  puts msg["subject"], msg["sender"], msg["received_at"]
  puts msg["body_text"]               # plain text body
  puts msg["body_html"]               # HTML body
  puts msg["otp_code"]                # extracted code, or nil
end
 
# drop one message, keep the inbox
first = res["emails"].first
MailFlat.call(Net::HTTP::Delete, "/inboxes/#{address}/messages/#{first['id']}")

JSON field	Type	What it is
subject	string	Subject line
sender	string	From address
body_text	string	Plain text body
body_html	string	HTML body
otp_code	string \| null	One-time code, extracted by us
to_address	string	The exact address it was sent to, tag included
tag	string \| null	Plus-addressing tag, if the sender used one
received_at	ISO 8601 UTC (ends with Z)	When it landed
is_encrypted	boolean	True on end-to-end encrypted inboxes, where body and code are unavailable

Sending mail from the inbox

Useful in reverse: point your own inbound pipeline at a MailFlat address and check that it handles what arrives.

On the Free plan you can send to your own addresses (your account email or any of your inboxes). To send anywhere else, connect and verify a domain. Free includes one; Pro plans include more.

Ruby

# mail leaves from the inbox address, DKIM-signed by our own MTA
MailFlat.call(Net::HTTP::Post, "/inboxes/#{address}/send", {
  to: "someone@example.com",
  subject: "Welcome",
  body: "Plain text body",
  html: "<p>Optional HTML body</p>",
})

Cleaning up

Ruby

MailFlat.call(Net::HTTP::Delete, "/inboxes/#{address}")
 
# or leave it: retention_hours on create means it cleans itself up
MailFlat.call(Net::HTTP::Post, "/inboxes", { prefix: "ci", retention_hours: 2 })

Two safety nets, use both

Delete in teardown so the list stays readable, and set retention_hours so a crashed run still cleans itself up.

In a test suite

Works with RSpec, Minitest, Capybara and anything else that gives you a setup and teardown hook.

Ruby

# spec/signup_spec.rb: a fresh inbox per example, torn down even on failure
require "securerandom"
 
RSpec.describe "Signup" do
  let(:address) do
    MailFlat.call(Net::HTTP::Post, "/inboxes",
                  { prefix: "ci-#{SecureRandom.hex(4)}", retention_hours: 2 })["address"]
  end
 
  after { MailFlat.call(Net::HTTP::Delete, "/inboxes/#{address}") }
 
  it "accepts a real verification code" do
    visit "/signup"
    fill_in "email", with: address
    click_button "Sign up"
 
    fill_in "code", with: MailFlat.wait_for_otp(address)
    expect(page).to have_current_path("/dashboard")
  end
end

Line by linewhat each step of this Ruby example does

unique prefix: One inbox per test, so parallel workers never read each other's mail.
teardown hook: Runs even when the test fails. That is exactly when inboxes get left behind.
real code, real email: No test-mode backdoor in your app: the path under test is the one your users take.

API reference

Endpoint	What it does	Returns
POST /api/v1/inboxes	Open an inbox, needs inbox:manage	{ ok, address, name, retention_hours }
GET /api/v1/inboxes	Every inbox this key opened	{ ok, inboxes: [...] }
GET /api/v1/inboxes/{address}/latest	Newest message, the polling call	{ ok, email: {...} \| null }
GET /api/v1/inboxes/{address}/messages	Every message, newest first	{ ok, emails: [...] }
POST /api/v1/inboxes/{address}/send	Send from this address	{ ok }
DELETE /api/v1/inboxes/{address}	Drop the inbox and its mail	{ ok }
DELETE /api/v1/inboxes/{address}/messages/{id}	Drop one message	{ ok }

Full endpoint reference, including error shapes and rate limits: Agent API and MCP.

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