Email server settings

Mailchimp SMTP settings for Mailchimp Transactional

Q: What are the Mailchimp SMTP settings?

Mailchimp Transactional: host smtp.mandrillapp.com, port 587 (or 25, 2525) with STARTTLS or 465 with SSL, any user name, and a Transactional API key as the password.

Q: Does Mailchimp have an SMTP server?

Yes, through Mailchimp Transactional (smtp.mandrillapp.com), a paid add-on for Standard and Premium plans that sends one-to-one transactional email. Bulk campaigns are sent from Mailchimp Marketing.

The Mailchimp SMTP settings belong to Mailchimp Transactional, a paid add-on for Standard and Premium plans: host smtp.mandrillapp.com, port 587 (or 25, 2525) with STARTTLS, or port 465 with SSL. The password is a Transactional API key; the user name can be any string.

Last checked October 10, 2026, against Mailchimp’s own documentation.

Mailchimp Transactional SMTP server and ports

Server, port and securityServer	Port and security
SMTP · outgoingsmtp.mandrillapp.com587 · STARTTLS	587STARTTLS
SMTP · outgoingsmtp.mandrillapp.com25, 2525 · STARTTLSSTARTTLS optional, as on 587; some hosts block port 25	25, 2525STARTTLS
SMTP · outgoingsmtp.mandrillapp.com465 · SSL/TLS	465SSL/TLS

Sign-in: Any user name + Transactional API key

User name: any string; Mailchimp recommends your account’s primary contact email. The password is a Mailchimp Transactional API key, not your web app password.

Mailchimp SMTP settings explained

From Mailchimp’s SMTP Integration docs:

Host: smtp.mandrillapp.com. You find it, with your credentials, on the SMTP & API Info page of Mailchimp Transactional.
Ports: 25, 587 or 2525 for non-encrypted connections, and “You can also use the STARTTLS extension (also known as TLS encryption) on these ports”; 465 for SSL. Using another port needs no configuration change in Mailchimp Transactional.
User name: “Any string (we recommend using the primary contact email on your Mailchimp account)”.
Password: “Any valid Mailchimp Transactional API key”.
Auth method: use login or plain in SMTP libraries. With Postfix, make sure an SASL library (such as libsasl2 or cyrus) is installed and up to date.

Mailchimp Transactional is “a paid add-on to a Standard or Premium monthly Marketing plan”; you buy blocks of credits at a recurring monthly rate (About Transactional Email). To add it, click Automations, then Transactional (Mailchimp).

Open the Settings of your Mailchimp Transactional account and find API Keys.
Click Create New Key, give it a description, and copy it at once; Mailchimp doesn’t show it again (Quick Start).
Paste the key into the SMTP password field of your app; enter your primary contact email (or any text) as the user name.

Test mode. With a test API key, no email is actually sent, and test messages don’t affect your account reputation. The limit is 10,000 test mode messages per day (Fundamentals). Use one while you build an integration.

Verify your sending domain first

Mailchimp Transactional “won’t send any email from unverified domains” or from domains without a valid DMARC policy and DKIM records (Authentication and Delivery). Verify ownership of the domain, then publish two DKIM CNAME records and a DMARC record of at least p=none:

mte1._domainkey.example.org  CNAME  dkim1.mandrillapp.com
mte2._domainkey.example.org  CNAME  dkim2.mandrillapp.com
_dmarc.example.org           TXT    "v=DMARC1; p=none"

A message rejected as unsigned “indicates that the sending domain hasn’t been properly set up”. Background: DKIM record, what is a DMARC record.

SMTP headers such as X-MC-Tags, X-MC-Metadata and X-MC-Track add tags, metadata and tracking options to a message. SMTP headers can be up to 1,000 characters long; Mailchimp suggests splitting larger merge data across several headers.

Common Mailchimp SMTP errors

Error or symptom	Fix
“Relay Access Denied”	Mailchimp lists it among the first errors new users see. Check that the password is a valid Transactional API key (not your web app password), that the app uses `login` or `plain` authentication and, with Postfix, that an up-to-date SASL library is installed.
“Unable to Connect to Host”	Make sure your hosting provider or ISP allows outbound SMTP connections; some hosts block port 25 or redirect the connection. Try another port (587, 2525 or 465).
Message rejected as `unsigned`	The sending domain isn’t verified or lacks the DKIM and DMARC records. Set them up as shown above.

To test the connection from your server, Mailchimp suggests Telnet on port 2525. A reachable server answers with a 220 line:

telnet smtp.mandrillapp.com 2525
220 smtp.mandrillapp.com ESMTP

Bounce codes from receiving servers: SMTP error codes.

Mailchimp Transactional or Mailchimp Marketing?

Mailchimp Transactional is “a delivery API that sends transactional emails and SMS messages from websites and applications”: it “sends email(s) to one recipient, triggered by the recipient’s action or inaction”. Bulk email to many recipients at once belongs in Mailchimp Marketing; Mailchimp’s SMTP documentation covers Mailchimp Transactional only.

Your Transactional account’s reputation is partly determined by your ratio of bounces, spam complaints and other factors to overall sending. Check addresses at sign-up with an email validation API so typos never turn into a hard bounce, and clean older lists with the bulk email verifier.

Sources

Checked on October 10, 2026. Server names, ports and sign-in rules come from these official pages:

Other SMTP relay services

Mailchimp SMTP settings: FAQ

What are the Mailchimp SMTP settings?

Mailchimp Transactional: host smtp.mandrillapp.com, port 587 (or 25, 2525) with STARTTLS or 465 with SSL, any user name, and a Transactional API key as the password.

Does Mailchimp have an SMTP server?

Yes, through Mailchimp Transactional (smtp.mandrillapp.com), a paid add-on for Standard and Premium plans that sends one-to-one transactional email. Bulk campaigns are sent from Mailchimp Marketing.

What is the Mailchimp SMTP username?

Any string. Mailchimp checks the API key in the password field and recommends your account’s primary contact email as the user name.

Why do I get “Relay Access Denied” from Mailchimp?

Usually the SMTP login isn’t accepted. Use a valid Mailchimp Transactional API key, not your web app password, with login or plain authentication.

Email validation API

Validate recipients before you send through Mailchimp

emailvalidation.io checks syntax, MX records and the mailbox over SMTP, flags disposable, role and free addresses and returns a quality score, in one request.

/v1/info Email validation API Read the documentation

100 free validations every month. No credit card required.

GET https://api.emailvalidation.io/v1/info?email=support@emailvalidation.io

{
  "email": "support@emailvalidation.io",
  "user": "support",
  "tag": "",
  "domain": "emailvalidation.io",
  "format_valid": true,
  "mx_found": true,
  "smtp_check": true,
  "catch_all": null,
  "role": true,
  "disposable": false,
  "free": false,
  "score": 0.64,
  "state": "deliverable",
  "reason": "valid_mailbox",
  "did_you_mean": ""
}

Free email tools

Is this a real email address? Check whether a mailbox exists, without sending an email. Email spam checker Will your email land in spam? Bulk email validator Which addresses on a list are deliverable? Email header analyzer Trace an email’s route and read its SPF, DKIM and DMARC results. Email extractor Pull every email address out of text or a CSV file. SPF record checker Is the SPF record valid? DMARC record checker Is the domain protected against spoofing? Disposable email checker Is this a throwaway address? Email syntax checker Is the address written correctly? MX record lookup Which servers receive mail for a domain? SPF record generator Build an SPF record and count its DNS lookups. DMARC record generator Create a DMARC record and see where it goes. DKIM record checker Is the DKIM key published? DKIM record generator Create a DKIM key pair and its DNS record. Scam email checker Check a sender for look-alike domains and other scam signals. Email blacklist checker Is your domain or mail server IP on a blacklist?