Mailsac vs Mailosaur

Mailosaur alternative for email testing

Mailsac gives QA and engineering teams test inboxes and a REST API for checking the email their apps send: sign-up confirmations, password resets and one-time codes. Here is how it compares with Mailosaur, including where Mailosaur is the better fit.

Reviewed September 2026 against both vendors’ public pricing and documentation.

Free plan: an API key, public inboxes, one private address and 1,500 Ops a month, with no expiry. Jump to the full comparison

At a glance

Free option

Mailsac Free plan, no expiry

Mailosaur 14-day free trial

Your own test domain

Mailsac Every paid plan, from $18 a month

Mailosaur Enterprise plan

SAML single sign-on

Mailsac Business, $89 a month

Mailosaur Enterprise, or a Core add-on

SMS, previews and spam checks

Mailsac Not offered

Mailosaur Yes; SMS and previews are add-ons

ISO 27001 and SOC 2

Mailsac None published

Mailosaur ISO 27001:2022, SOC 2 Type I

Which should you choose?

Both let automated tests receive the email your app sends and check what is in it. Whether Mailsac is the right Mailosaur alternative depends on what else you need to test, and how your company buys software.

Choose Mailsac if

Your tests need email only, and you want test addresses on your own domain, or on a subdomain you name, such as yourteam.msdc.co, with no DNS changes. Either is included in self-serve plans from $18 a month.
You need SAML single sign-on at a published price. Business is $89 a month and includes 5 team logins.
You want a free plan that doesn’t expire, with public inboxes for quick checks using made-up data.
Procurement wants a published Enterprise price: $3,540 a year, payable by purchase order or through resellers such as SHI and SoftwareOne.

Choose Mailosaur if

You also test SMS codes or authenticator-app (TOTP) logins.
You need email previews on real devices, client compatibility and accessibility checks, or deliverability reports covering SPF, DKIM, DMARC, blocklists and SpamAssassin.
Your security review asks for ISO 27001 or SOC 2 reports, or for data hosted in the UK or EU.
You need single sign-on through OpenID Connect, or SCIM user provisioning. Mailsac’s single sign-on is SAML only.
You want client libraries in seven languages that wait for the message and pull out codes and links for you, or tests that reply to and send email.

Mailsac vs Mailosaur: features and prices

Prices are list prices in US dollars, before tax, as each vendor shows them. The plans measure usage in different units, so compare by the job you need done.

Plans and prices
	Mailsac	Mailosaur
Free option	Free plan with no expiry: API key, public inboxes, 1 private address, 1,500 Ops a month	14-day free trial
Entry plan	Indie: $18 a month, or $169 a year	Personal: $25 a month, or $20 a month billed annually
Team plan	Business: $89 a month, or $840 a year. 5 team logins	Core: $62.50 a month, or $50 a month billed annually. 5 seats
Enterprise	From $3,540 a year, published. Invoice, purchase order, ACH or wire; also sold by resellers SHI and SoftwareOne	Custom pricing through sales. Invoice payment on Core and Enterprise; reseller partner programme
Included usage	Ops a month: 25,000 on Indie, 2 million on Business. An Op is an API call, an inbound message to a private address or domain, or a forwarded message; a polled test typically uses 3 to 6	Inbound emails: 500 a day on Personal, 2,500 a day on Core
Addresses and domains
Test addresses with no setup	Any `@mailsac.com` address (public), or any address on your custom domain (private)	Any address on each inbox’s own `ID.mailosaur.net` domain
Your own receiving domain	Indie and up: 1, 5 or 12+ custom domains. Each can be your own domain or a `yourteam.msdc.co` subdomain that needs no DNS changes	Enterprise plan
Test automation
Official client libraries	JavaScript/TypeScript client and a Cypress plugin; any other language over REST	Node.js, Java, Python, .NET, Ruby, PHP and Go
Waiting for new mail	Poll the REST API on any plan, or have private addresses and domains push new mail to a WebSocket or webhook. The Cypress plugin waits for you	The client libraries’ get method waits for a matching message
Codes and links	Mailsac extracts links; your test matches codes (the Cypress plugin has `extractCode`)	Mailosaur extracts both codes and links
SMTP capture for staging	Email Capture on every plan; captured mail is public unless you turn on private capture	An SMTP server for each inbox
Beyond receiving email
SMS and authenticator (TOTP)	Not offered	“SMS and authentication” add-on, from $37.50 a month
Previews and HTML checks	Not offered	Real-device previews add-on, from $25 a month. Client compatibility checks; accessibility checks on Core
Deliverability checks	Not offered	Report covering SPF, DKIM, DMARC, blocklists and SpamAssassin
Replying and sending	Receive only. Forwards new mail to a webhook, WebSocket, Slack or another Mailsac address	Reply and send to outside addresses on Core
Security and access
Single sign-on	SAML, on Business and Enterprise	SAML or OpenID Connect on Enterprise, or as a Core add-on. SCIM on Enterprise
Certifications and hosting	None published. Runs on AWS. Enterprise includes help with SIG and CyberGRX security questionnaires	ISO 27001:2022, SOC 2 Type I, PCI DSS (SAQ A). Hosted on Google Cloud in the UK and EU

Reviewed September 24, 2026. Mailosaur’s plans count inbound emails per day; Mailsac’s count Ops per month, including API calls. Check each vendor’s current pricing before you buy.

Sources: Mailosaur pricing, inboxes, domains, single sign-on, API, SMS, compliance checks, deliverability, security and trust center. Mailsac pricing, Enterprise and custom domains.

How an email test works in Mailsac

Your app sends the email as usual. Your test reads it back over HTTPS with a Mailsac-Key header. No inbox has to exist first.

Trigger. Your test makes your app email a unique address, such as signup-<run-id>@yourteam.msdc.co, and notes the time.
Wait. Poll GET /api/addresses/{email}/messages every second or two until a message newer than the trigger arrives, up to a deadline. Or have a private address or domain push new mail to a WebSocket or webhook.
Check. Search the plain text for the code, or use the links Mailsac extracted, and assert on them.

Coming from Mailosaur? Its client libraries wait for the message and extract codes for you. With Mailsac, your test polls and keeps mail received after the trigger, or the @mailsac/cypress plugin does that with cy.mailsacWaitForMessage(). Codes are matched in your test code.

List an inbox, then print its newest message · bash or zsh, needs curl and jq

EMAIL="signup-test-1234@mailsac.com"
MESSAGES=$(curl -fsS -H "Mailsac-Key: $MAILSAC_API_KEY" \
  "https://mailsac.com/api/addresses/$EMAIL/messages?limit=10")
jq '.[] | {_id, received, subject}' <<< "$MESSAGES"
MESSAGE_ID=$(jq -r '.[0]._id // empty' <<< "$MESSAGES")
if [ -n "$MESSAGE_ID" ]; then
  curl -fsS -H "Mailsac-Key: $MAILSAC_API_KEY" \
    "https://mailsac.com/api/text/$EMAIL/$MESSAGE_ID"
else
  echo "Nothing to read for $EMAIL yet"
fi

Set EMAIL to the address your app emailed. Keep MAILSAC_API_KEY in shell or CI secrets, never in browser code.

Public and private inboxes

Mail sent to an @mailsac.com address is public by default. Anyone can view a public inbox on the Mailsac website without an account, and any Mailsac API key can read it. Public inboxes are temporary, and they are fine for trying things out with made-up data.

For password-reset links, codes and anything else that works on a real account, use a private address (the free plan includes one) or a custom domain: a msdc.co subdomain, or your own domain once it is verified. Only your account and team can read that mail. It is the closest match to a Mailosaur inbox, which belongs to your account and whose project controls who can see it.

The same applies to SMTP capture: captured mail is public unless you turn on private capture or capture to a private domain. And some sign-up forms reject well-known testing domains; the public disposable-email-domains list includes both mailsac.com and mailosaur.net. A domain of your own avoids that.

Public inboxes are for synthetic test data. If a reset link or code would work on a real account, or the email holds real personal data, use a private address or a verified private custom domain.

Try Mailsac with your next email test

Create a free account, generate an API key and run the example above. Plans with a private test domain start at $18 a month.

Also comparing Mailtrap? Read Mailsac vs Mailtrap. New to Mailsac? See how the email testing API works.