Mailchimp A transactional email is the automated message a WordPress site sends in response to a single user action – a password reset, an order confirmation, a form receipt – addressed to the user who triggered it. Read full reference → is the rebranded Mandrill service: Mandrill’s sending infrastructure, sold as an add-on to Mailchimp’s marketing platform. The rebrand is on the bill, not on the wire. The SMTP host is still smtp.mandrillapp.com, the API is still at mandrillapp.com, the SPF include is still spf.mandrillapp.com, and the DKIM selector is still mandrill._domainkey. A WordPress operator who arrived here looking for Mandrill is in the right place.
For a site already paying for Mailchimp Standard, the marginal cost of a 25,000-email block is reasonable. For everyone else, the platform fee buys nothing they will use. Sites already on Standard get transactional sending for $20/month per block ($0.0008 per email at full use). Sites sending over 100,000 messages per month see the per-block price step down toward $10 at four million per month, which makes Mandrill cost-competitive at scale. Sites in between, which is most WordPress operators, pay the $40/month minimum for capacity they will not use and would pay less at Postmark (the right default at that volume), SMTP2GO (free up to 1,000 emails per month), or Brevo (free up to 300 emails per day).
Mandrill itself dates to 2008 and was acquired and rebranded by Mailchimp in 2016. The infrastructure has not meaningfully changed; the pricing model has. The product targets two audiences: existing Mailchimp customers consolidating onto one platform, and high-volume transactional senders. For WordPress sites in neither group, the alternatives above match the workload more cleanly.
SMTP settings
| Setting | Value |
|---|---|
| Host | smtp.mandrillapp.com |
| Port | 587 (recommended, STARTTLS); also 25, 2525, and 465 (SSL) |
| Encryption | STARTTLS on 587, 25, 2525; SSL on 465 |
| Authentication | PLAIN or LOGIN |
| Username | The email address on the Mailchimp account |
| Password | A Mailchimp Transactional API key |
The Transactional API key is generated under the Mailchimp Transactional dashboard, not the main Mailchimp marketing API key area; the marketing key will not authenticate SMTP. The generated key displays once at creation, so store it immediately.
Mandrill’s HTTPS API endpoint (https://mandrillapp.com/api/1.0/) is the other integration path. WordPress mailer plugins with a dedicated Mandrill option use the API rather than SMTP, which skips the SMTP handshake on every send.
DNS authentication
Sending production email through Mandrill requires DKIM signing and an SPF record on the sending domain. Mandrill’s dashboard publishes the exact records to add.
DKIM. A TXT record at mandrill._domainkey.<your-domain>. The key value is generated per-domain in Mandrill’s 
sending domain settings.
SPF. Add include:spf.mandrillapp.com to the existing SPF record at the apex of the sending domain. If the domain has no SPF record, the minimum policy is v=spf1 include:spf.mandrillapp.com -all. If the domain already authorises other senders (Google Workspace, a second relay), add the Mandrill include without removing the existing ones; SPF allows up to ten DNS-lookup-incurring mechanisms in total.
DMARC. Not Mandrill-specific, but Gmail and Yahoo require a published DMARC policy from senders exceeding 5,000 daily messages to either platform. p=none is the safe starting point for monitoring before tightening to p=quarantine or p=reject.
After publishing each record, verify with swaks that test messages authenticate cleanly before routing production traffic.
Pricing
Mailchimp Transactional Email is an add-on to Mailchimp’s marketing platform. It cannot be purchased independently. The minimum cost combines a Mailchimp Standard plan and at least one email block.
| Component | Cost | Notes |
|---|---|---|
| Mailchimp Standard plan | $20/month | Required prerequisite; Free and Essentials tiers do not qualify |
| Email block | $20 per 25,000 emails | Smallest purchasable unit |
| Dedicated IP (optional) | $29.95/month | Add-on |
Email blocks scale down with volume:
| Blocks | Volume | Price per block |
|---|---|---|
| 1-20 | Up to 500,000 | $20 |
| 21-40 | 500,000-1,000,000 | $18 |
| 41-80 | 1,000,000-2,000,000 | $16 |
| 81-120 | 2,000,000-3,000,000 | $14 |
| 121-160 | 3,000,000-4,000,000 | $12 |
| 161+ | 4,000,000+ | $10 |
Unused blocks do not roll over. A WordPress site sending 2,000 transactional emails in a month pays the same $40 minimum as a site sending 25,000. New accounts receive an allowance of 500 demo emails to a verified domain before any block is required, which is enough to validate connection and authentication but not enough to run live traffic.
Cost comparison
Among providers covered in nanoPost’s transactional email overview, Mailchimp Transactional Email has the highest entry point for typical WordPress volumes. Postmark Basic is $15/month for 10,000 emails with no platform subscription. SMTP2GO includes 1,000 emails per month on its free tier indefinitely. Brevo (formerly Sendinblue) includes 300 emails per day on its free plan. Mailgun Basic is $15/month at the 10,000-email tier.
The crossover where Mandrill becomes price-competitive is volume-dependent. At 4 million emails per month, the per-email cost drops to $0.0004 inside the block; the Standard plan fee becomes a rounding error at that scale. At that point Mandrill matches or undercuts Mailgun and approaches Amazon SES territory. For the typical WordPress site sending under 10,000 emails per month, the crossover never arrives.
The Mailchimp platform bundle
The defining feature of Mailchimp Transactional Email is what it is not sold as: a standalone product. The service lives inside Mailchimp’s marketing platform, sharing account infrastructure, billing, and dashboard with Mailchimp’s audience-management and campaign tools. For sites already running Mailchimp for marketing, this is the point: one account, one bill, one place to manage all email traffic.
For transactional-only WordPress sites, the bundle is overhead. The Standard plan’s marketing features (audience segmentation, automation builders, campaign reports) sit unused. The Mailchimp Transactional dashboard is a separate area inside the same account, with its own activity log, sending domains, webhook configuration, and template store. Activity logs retain 30 days of message-level data, which covers most debugging cases and falls short of Postmark’s 45 days on Basic or its multi-month retention on Pro.
WordPress sites that need to react programmatically to delivery failures can subscribe to Mandrill webhooks; the events covered include bounces, complaints, deferrals, opens, and clicks. The webhook configuration lives in the Transactional dashboard, not in the marketing platform.
Templates designed in Mailchimp’s marketing builder can be published into the transactional service and addressed by name from the API. Most WordPress sites will not use this; WordPress core, WooCommerce, and most form plugins generate their own HTML. Templates matter for custom integrations where the sending application stores message structure outside WordPress.
WordPress integration: Mandrill plugins and SMTP
Three paths connect Mailchimp Transactional Email to WordPress.
Generic SMTP via any mailer plugin. WP Mail SMTP, FluentSMTP, Post SMTP, and other mailer plugins accept arbitrary SMTP settings. Use the values from the SMTP settings table above. The username is the Mailchimp account email; the password is the Transactional API key, not the marketing API key. This path works with every mailer plugin and survives switching between them.
WP Mail SMTP’s dedicated Mandrill mailer. WP Mail SMTP includes a built-in Mandrill option that uses the Mandrill API directly rather than SMTP. The setup is shorter (no host or port to configure, only the API key), and per-send latency is lower because the SMTP handshake is skipped. The trade-off: the configuration is locked to WP Mail SMTP, so migrating to another mailer plugin later means reconfiguring.
The Send Emails with Mandrill plugin. Send Emails with Mandrill by Miller Media is a community-maintained fork of the original wpMandrill plugin. It replaces wp_mail() with a Mandrill API call and falls back to native wp_mail() if the API send fails (useful only where wp_mail() itself works). Tagging and template-routing controls are exposed for sites that use Mandrill’s analytics or template features.
For most WordPress sites, the generic SMTP path is the most portable choice. Sites already standardised on WP Mail SMTP benefit from the dedicated Mandrill mailer. Sites that want Mandrill-specific tagging or the wp_mail() fallback should pick Send Emails with Mandrill.
The verdict
Mailchimp Transactional Email fits two specific cases. Sites already paying for Mailchimp Standard get transactional email for the marginal cost of a 25,000-email block, which is reasonable. High-volume transactional senders moving over 100,000 messages per month see the block-tier discounts compound into competitive per-message economics, with Mandrill’s well-established delivery reputation behind them.
For every other WordPress site, which is most of them, the $40/month minimum buys capacity that will sit unused and a platform fee for marketing features that will not be touched. Postmark is the better default for transactional WordPress under 100,000 messages per month. SMTP2GO and Brevo cover the low-volume and free-tier cases. The Mandrill infrastructure is sound; the pricing model is what decides whether it fits.
For the broader setup that places Mailchimp Transactional Email inside the WordPress email stack, see the WordPress email setup guide.