Postmark SMTP Configuration
Use these exact values when configuring any email client or application to send through Postmark servers.
| Parameter | Value |
|---|---|
| SMTP Host | smtp.postmarkapp.com |
| SMTP Port | 587 (TLS) or 25 (TLS) |
| Encryption | STARTTLS on port 587 or 25 |
| Username | Your Postmark Server API Key (Server ID) |
| Password | Your Postmark SMTP API Token |
Note: Postmark uses an unusual authentication model where the username is your Server ID (a number) and the password is a SMTP-specific API token. Both are found in your Postmark server settings under "SMTP Credentials."
Step-by-Step Setup
Follow these steps in order to configure SMTP access for Postmark.
1. Create a Postmark Server
Create a Postmark account and set up a server for your application. Each server gets a unique Server ID and can have multiple SMTP tokens for different applications.
2. Add a Sender Signature
Before sending, add and verify a sender signature (From email address) in your Postmark server. Postmark requires verified sender addresses for all outgoing email.
3. Create SMTP Credentials
In your Postmark server, go to "SMTP Credentials" and create a new token. Copy the Server ID (username) and the SMTP token (password). You can create multiple tokens per server.
4. Configure Your Application
Enter smtp.postmarkapp.com as the SMTP host, port 587 with TLS, your Server ID as the username, and your SMTP token as the password.
Common Errors and Solutions
Most Postmark SMTP issues fall into a handful of categories. Here's how to fix them quickly.
Invalid Credentials
Postmark uses your Server ID as the username and a separate SMTP token as the password. Make sure you're using SMTP credentials specifically, not your main Postmark API token.
Sender Not Verified
Postmark requires all sender addresses to be verified before sending. Add your From address in your Postmark server's "Sender Signatures" section and complete the verification process.
Connection Timeout
Port 587 may be blocked by your network. Try port 25 with TLS as an alternative. Postmark supports both ports for TLS connections.
Inactive Server
Postmark servers can be suspended if your sending reputation drops too low or if there are payment issues. Check your Postmark account for any suspension notices.
Best Practices for Postmark SMTP
Keep your account secure and your messages deliverable with these recommended approaches.
Use Separate SMTP Tokens
Create unique SMTP tokens for each application rather than sharing credentials. This allows granular revocation if a specific application is compromised.
Verify All Sender Addresses
Add and verify all sender addresses you plan to use. Postmark's verification process is straightforward and helps maintain your sending reputation.
Use the API for Better Features
Postmark's SMTP provides basic sending, but their API offers better features including detailed delivery webhooks, open/read tracking, and bounce handling without additional configuration.
Keep Credentials Secure
Store SMTP tokens in environment variables or a secrets manager. Don't hardcode credentials in source code. Rotate tokens if there's any suspicion of compromise.
When Postmark SMTP Needs an Alternative
Postmark is a well-regarded transactional email service with excellent deliverability, but their SMTP offering is relatively basic compared to their API. If you need advanced features like webhook-based routing, detailed analytics, and intelligent delivery optimization, Postmark's API is more capable than their SMTP interface.
For teams needing predictable pricing with better features, an SMTP relay service may offer more value. Learn more about email deliverability and how proper configuration affects inbox placement.
Frequently Asked Questions
What are Postmark's SMTP sending limits?
Postmark plans range from 100 emails/month on free tier to millions on enterprise. Limits are per server and per account. Contact Postmark support for higher volume increases.
Can I use Postmark with custom domains?
Yes. Add your custom domain as a sender signature in your Postmark server and complete DNS verification. Once verified, you can send from any address on that domain.
My Postmark SMTP is being rejected. What should I do?
Verify you're using the Server ID as username and an SMTP token as password (not the API token). Confirm your sender address is verified in your Postmark server. Check your server isn't suspended.
Is Postmark suitable for transactional emails?
Yes, Postmark is excellent for transactional email. Their SMTP works well, but their API offers more features including webhooks, open tracking, and bounce handling. Postmark has a strong reputation for deliverability.
How do I create multiple SMTP tokens in Postmark?
In your Postmark server, go to SMTP Credentials and click "Create SMTP token." Each token can be labeled for identification and revoked independently without affecting other tokens.
Ready to move to reliable email infrastructure?
Start free with no card, or talk to sales for high-volume and enterprise.
Start SendingTalk to Sales