Mailjet SMTP Settings and Configuration (2026)
Native SMTP relay with unified API/SMTP credentials
Mailjet is a European-headquartered email platform (Paris) now part of the Sinch group — same parent as Mailgun. It combines transactional and marketing email in one product, aimed at teams where developers and marketers work side-by-side. Distinctive design choice: your API Key and Secret Key work for both the REST API and the SMTP relay — a single credential pair, unlike Postmark or Mailgun which issue separate SMTP-only tokens.
Mailjet offers a persistent Free tier at 6,000 emails/month capped at 200/day, making it one of the more generous free plans among transactional providers. EU data hosting is available for GDPR-sensitive use cases — a differentiator against US-based SendGrid, Postmark, and Amazon SES. Owned by Sinch since 2019 alongside Mailgun and Inbox (the Sinch email portfolio).
Quick reference
The essential Mailjet SMTP settings. Same host globally — no region selection in the SMTP interface.
| SMTP server | in-v3.mailjet.com GLOBAL |
|---|---|
| SMTP port (STARTTLS) | 587 RECOMMENDED |
| SMTP port (SSL/TLS) | 465 |
| Alternative ports | 2525, 588, 80 (fallbacks if 587/465 blocked) |
| Username | Your API Key (public identifier) |
| Password | Your Secret Key (private, shown once at creation) |
| Message size cap | 15 MB (includes base64-encoded attachments) |
| Sender verification | Verified sender address OR verified domain (SPF + DKIM) |
SMTP configuration
Outgoing mail server
— sending transactional and marketing email
Setup steps
- Sign up at mailjet.com. The Free tier gives you 6,000/month at 200/day permanently — enough for most side projects and pre-production apps.
- Navigate to Account › API Key Management (or SMTP & API Keys from the dashboard). Locate your Primary API Key and click Generate Secret Key. Copy both values immediately — the Secret Key is displayed only once.
- Verify your sending domain: Account Settings › Domains & Sender addresses › SPF/DKIM Authentication. Mailjet generates a 2048-bit DKIM public key with auto-rotation option. Add the TXT record at
mailjet._domainkey.your-domain.comto your DNS. Optionally add the SPF include for basic SPF validation (not required for DKIM-only DMARC alignment). - In your email client or WP SMTP plugin, enter host
in-v3.mailjet.com, port 587, encryptionSTARTTLS, username = your API Key, password = your Secret Key. - Send a test email using a
From:address on your verified domain. Check Statistics › Message events in your Mailjet dashboard for delivery confirmation and any bounce or spam classification. - If sending fails after successful authentication with a policy error, your new account may still be under review — Mailjet restricts new accounts to verified recipient addresses until account verification completes. Contact Mailjet support if this persists beyond 48 hours.
Authentication and subaccounts
Mailjet’s unified credential model is unusual: the same API Key + Secret Key pair authenticates both the SMTP relay (as username and password) and the REST API v3/v3.1. This simplifies onboarding but means a leaked SMTP credential also compromises API access.
Subaccounts via multiple API Keys
Create additional API Keys from API Key Management to spin up subaccounts — nested accounts under your primary Mailjet account, each with a distinct API Key. Useful for agencies (one subaccount per client), multi-brand senders (per-brand isolation), or environment separation (Prod/Staging). Each subaccount has its own statistics and reputation tracking.
Secret Key rotation
Mailjet recommends rotating the Secret Key every 90 days. Resetting a Secret Key requires updating authentication in all active SMTP and API connections — plan a rotation window. If you suspect credential compromise, rotate immediately.
SPF and DKIM setup
Domain verification unlocks DKIM signing, which is required for reliable inbox placement under Gmail and Yahoo’s 2024 bulk sender requirements. Wizard location: Account Settings › Domains & Sender addresses › SPF/DKIM Authentication.
DKIM record (TXT)
Mailjet publishes a 2048-bit DKIM public key at mailjet._domainkey.your-domain.com. Key auto-rotation available via Account › Domains › Regenerate Key. Format:
Type: TXT · Host: mailjet._domainkey · Value: k=rsa; p=MIGfMA0GCSqGSIb3DQEBA...QIDAQAB
SPF record (optional)
v=spf1 include:spf.mailjet.com ~all
Adding the SPF include is not mandatory for DMARC alignment — DKIM alone signed by your domain is sufficient. Include it only if your DMARC policy requires SPF pass regardless of alignment.
DMARC alignment
With DKIM signed by your domain, relaxed DMARC alignment works out of the box (DKIM pass with domain match). Strict DMARC alignment via SPF requires a custom Return-Path configuration — contact Mailjet support for advanced setup. Publish at least v=DMARC1; p=none; rua=mailto:reports@your-domain.com; sustained non-alignment triggers hard failures at Gmail and Yahoo for senders above 5,000/day.
Rate limits & sending caps
| Limit type | Value | Notes |
|---|---|---|
| Free plan volume | 6,000/month | Permanent free tier — not a trial. Persistent as long as account is active. |
| Free plan daily cap | 200/day | Hard daily cap on Free plan. Overage is queued and released the next day. Queued mail is deleted after 3 days if never released. |
| Message size (total) | 15 MB | Includes base64-encoded attachments (roughly 1/3 larger than the file on disk). |
| REST API v3.1 batch limit | 50 messages/call | Applies to /v3.1/send batch endpoint. SMTP has no explicit batch equivalent. |
| Rate limit exceeded response | HTTP 429 | Retry with exponential backoff. Throughput scales with plan tier. |
| Dedicated IP | Available on higher-volume plans | Progressive warmup 2-6 weeks recommended. Available from Premium/Enterprise tiers. |
Paid plans (Essential, Premium, Custom) unlock higher volumes, remove Mailjet branding, add advanced segmentation, dedicated IP, and dedicated support. Paid tier pricing scales with monthly send volume — contact Mailjet sales for volumes above 500k/month.
Common setup gotchas
Using your account login password instead of Secret Key
The SMTP password is your Secret Key from the API keys page — NOT your Mailjet account login password. This is the single most common Mailjet setup failure. Symptom: 535 Authentication failed after the login banner. Fix: go to Account › API Key Management, click Show on the Secret Key (or Generate a new one if lost), use that value.
Secret Key is shown only once at generation
When you create an API Key or regenerate its Secret Key, the Secret Key is displayed only once. If you did not copy it immediately, there is no recovery path — you must generate a new Secret Key, which invalidates the old one and breaks any active connection using it. Store the Secret Key in your secret manager or password vault at creation time.
Free plan hard daily cap at 200/day — not a rolling average
The 200-emails-per-day Free plan cap is a hard daily ceiling, not a rolling 24-hour window. Once you hit 200 in a calendar day, additional sends are queued and released the next day at UTC midnight. Queued emails are deleted after 3 days if not released. Plan for spike smoothing on Free tier — a marketing burst that exceeds 200 will silently lose email after 3 days if you do not track the queue.
API Key and Secret Key double as REST API credentials
Unlike Postmark or Mailgun which issue separate SMTP-only credentials, Mailjet uses one API Key + Secret Key pair for both SMTP relay and REST API access. This simplifies onboarding but means a leaked SMTP credential grants full API access — including reading statistics, modifying campaigns, and creating subaccounts. Rotate immediately on suspicion of compromise.
New accounts may be restricted to verified recipients
Mailjet places new accounts under review and may restrict outbound to only verified recipient addresses until account verification completes. Symptom: authentication succeeds, message accepted, but delivery fails with a policy error and the message never reaches unverified recipients. Fix: complete identity verification in your dashboard, or contact Mailjet support if verification takes longer than 48 hours.
Port 25 is not encrypted by default — blocked on most cloud hosts
Port 25 on Mailjet transmits credentials in the clear unless STARTTLS is enforced by your client. Combined with the fact that AWS EC2, DigitalOcean, Heroku, and Google Cloud block outbound port 25 by default, there is no reason to use it. Standard choices: 587 (STARTTLS, recommended), 465 (implicit SSL/TLS), 2525 or 80 as fallbacks on restrictive networks.
Migrating SMTP setups
To Mailjet (from another provider)
Update your app’s SMTP config to in-v3.mailjet.com:587 and use your API Key as username, Secret Key as password. Verify your sending domain via Account Settings › Domains & Sender addresses and add the DKIM TXT record to your DNS. Plan for 15 minutes to 4 hours of DNS propagation. If you need per-brand or per-client isolation, create subaccounts via additional API Keys. Keep your old provider active during the parallel run.
From Mailjet (to a different provider)
Common triggers: cost at scale (Mailjet pricing grows steeply above 100k/month), need for stricter transactional-only deliverability, or preference for a US-based provider. Postmark for premium transactional-only with best-in-class deliverability. SendGrid for broader ecosystem with Marketing Campaigns at similar pricing tiers. Amazon SES for aggressive cost optimization above 50k/month if your team has AWS operational maturity. Brevo if you want an EU-based alternative with a similar developers-and-marketers unified model.
Frequently asked questions
What is Mailjet’s SMTP server address?
Mailjet uses a single global SMTP host: in-v3.mailjet.com. There are no regional variants — the host resolves to Mailjet’s global infrastructure. Recommended port is 587 with STARTTLS. Alternatives: 465 (SSL/TLS), 2525, 588, and 80 for restrictive networks. Legacy hostnames like in.mailjet.com are deprecated — always use in-v3.mailjet.com.
What credentials do I use to authenticate to Mailjet SMTP?
Use your API Key as the SMTP username and your Secret Key as the SMTP password. Both are found at Account › API Key Management (or SMTP & API Keys from the dashboard). Do NOT use your Mailjet account login password — that is not accepted by the SMTP relay. The same API Key + Secret Key pair works for both SMTP and the REST API v3/v3.1.
How much does Mailjet cost?
Free plan: 6,000 emails/month capped at 200/day, permanent (not a trial). Paid plans (Essential, Premium, Custom) scale with monthly send volume, unlock higher throughput, remove Mailjet branding from footers, add advanced segmentation and dedicated IP. Enterprise-tier pricing is negotiated for volumes above 500k/month. EU data hosting is available on paid tiers — useful for GDPR-sensitive senders.
What is the difference between Mailjet and Mailgun?
Both are owned by Sinch since 2019. Mailgun is developer-first, API-oriented, US-based (with EU region available), designed for high-volume transactional infrastructure. Mailjet is developer-and-marketer, EU-headquartered (Paris), with unified transactional + marketing email in one product and a more generous permanent Free plan (6,000/month vs Mailgun’s 30-day trial). Pick Mailgun for pure transactional API-first setups with EU region needs, Mailjet for teams where marketers use the same platform as developers.
Does Mailjet support IMAP or POP3?
No. Mailjet is a send-only SMTP relay and marketing platform. IMAP and POP3 are protocols for retrieving mail from a mailbox, and Mailjet does not host mailboxes. Mailjet does support inbound email processing via the Parse API (POST incoming mail as JSON to your webhook), but this is a receive-and-process pattern for building email-triggered workflows, not a mailbox you read with a mail client.
Why should I use Mailjet over SendGrid, Mailgun, or Brevo?
Pick Mailjet if any of these matter: (1) EU data hosting is required for GDPR compliance and you prefer an EU-headquartered provider; (2) your team needs transactional and marketing email in one product without integration overhead; (3) you value a persistent 6,000/month Free tier over 30-day trials; (4) you want the same API Key + Secret Key pair to authenticate both SMTP and REST API. Do NOT pick Mailjet if you send above 500k/month at cost-sensitive tiers — Amazon SES or Mailgun scale cheaper. Also skip Mailjet if you need best-in-class transactional-only deliverability — Postmark wins that use case.
This review follows our email infrastructure testing methodology. We disclose affiliate relationships in our editorial independence policy.
