Postmark SMTP Settings
Transactional email service from ActiveCampaign, tuned for speed over bulk volume.
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Outgoing mail (SMTP)
SMTP server
smtp.postmarkapp.com
Port. STARTTLS
587
Security
STARTTLS on 587 (recommended), 2525 or 25. Postmark does not offer SSL/TLS on 465.
Incoming mail (IMAP)
IMAP
Not supported. This is a send-only service.
Incoming mail (POP3)
POP3
Not supported by this provider.
Sending limits & login
Daily send limit
Set by your Postmark plan.
Authentication
Use your Server API Token as both the SMTP username and the password.
App password
Find the token under your Postmark server > API Tokens, or create a dedicated SMTP token per message stream.
Postmark is a send-only relay: there is no IMAP or POP inbox. Use port 2525 if your host blocks 587.
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Postmark SMTP, IMAP and POP3 settings
Postmark is a transactional email service, owned by ActiveCampaign since 2022, built around fast delivery of receipts, password resets and other one-to-one mail. It has no implicit SSL port, so port 465 will never connect; you use 587, 2525 or 25 with STARTTLS. Your Server API Token is typed into both the username and password fields.
Postmark is a send-only relay, so there's no IMAP or POP3 inbox. You only configure the SMTP server above. Use the tool to copy each value into your app or script.
Checked against Postmark's own documentation: postmarkapp.com. Ports and limits change, so check there too if something will not connect.
Postmark settings at a glance
One card with every server and port on it. Right click to save it, or share the page and this is the preview people see.
What to enter as your Postmark username and password
Wrong credentials, not a wrong port, are the usual reason a Postmark connection fails. These are the exact values to type.
Your Server API Token, or the Access Key if you created an SMTP token
The same Server API Token again, or the matching Secret Key if you created an SMTP token
Get your server api tokenHow to set up Postmark in a mail client
The exact path through Postmark's own settings, in order.
- 1
Wait for account approval
Postmark reviews every new account by hand, usually in under 24 hours on weekdays. Until it clears you can only send to domains you have added and verified, plus test@blackhole.postmarkapp.com.
- 2
Verify the From address
Add the address as a Sender Signature, or verify the whole domain, in the Postmark dashboard. Mail from an unverified address is rejected.
- 3
Turn SMTP on for the server
SMTP access is enabled or disabled per server on that server's Settings page, so check it is on before you test.
- 4
Copy the Server API Token
Open your server at https://account.postmarkapp.com/servers and use the API Tokens tab. This is the server-level token, not the account-level one.
- 5
Connect to smtp.postmarkapp.com
Use port 587, 2525 or 25 with STARTTLS. For broadcast message streams the host is smtp-broadcasts.postmarkapp.com instead.
What Postmark looks like filled in
Every mail client asks for the same handful of fields. Here they are with Postmark's values already in place.
Account settings: Postmark
Server
smtp.postmarkapp.comPort
587Encryption
STARTTLSAuthentication
RequiredUsername
Your Server API Token, or the Access Key if you created an SMTP tokenPassword
The same Server API Token again, or the matching Secret Key if you created an SMTP tokenIMAP / POP3
Not applicable. Postmark sends only, so there is no inbox to configure.An illustration of the fields, not a screenshot of any one app. Field names differ slightly between Outlook, Apple Mail and Thunderbird; the values do not.
Postmark SMTP settings in Thunderbird
The outgoing server dialog with Postmark's details entered. Outlook and Apple Mail ask for the same four things under slightly different names.
Which port should you use for Postmark?
STARTTLS on 587 (recommended), 2525 or 25. Postmark does not offer SSL/TLS on 465.
STARTTLS
Starts as a plain connection, then upgrades to an encrypted one. The modern standard for sending.
SSL/TLS
Postmark does not accept SSL/TLS on 465. Use the STARTTLS port instead.
Plain SMTP
Meant for server-to-server relay. Home networks and cloud hosts block it, so do not use it to send from a client.
Why your Postmark connection is failing
The failures people actually hit with Postmark, and what fixes each one.
Postmark does not offer implicit SSL on 465 at all. Move the client to port 587, 2525 or 25 and switch encryption to STARTTLS.
The From header must exactly match an address or domain showing a verified status in your Postmark account. Add and confirm it, then resend.
That address hard bounced or filed a spam complaint and is now suppressed. Hard bounces and unsubscribes can be reactivated yourself from the message stream's Suppressions tab; a spam complaint has to be reactivated by Postmark support.
This is the manual approval hold, not a configuration fault. Wait for the review, and email support@postmarkapp.com with sample messages if it is declined.
SMTP needs the Server API Token from Servers, then your server, then the API Tokens tab. The account-level token is for account API calls, not for sending.
Postmark sending limits
Postmark asks customers to keep to 10 concurrent SMTP connections per IP and says it does not enforce that in software; the text and HTML bodies are separately capped at 5 MB each.
Per day
No published daily cap
Recipients per message
50 recipients per message, counting To, Cc and Bcc together
Max attachment
10 MB total message size including attachments, measured after base64 encoding
Postmark servers by region and plan
Postmark does not use one set of hostnames everywhere. Match the row to your account.
| Region or plan | SMTP | IMAP | POP3 |
|---|---|---|---|
| Broadcast message streams | smtp-broadcasts.postmarkapp.com | Not applicable | Not applicable |
Postmark quirks by mail client
Apple Mail
Apple Mail's default of SSL on port 465 will not connect to Postmark, so set the outgoing server to port 587 and let it negotiate TLS through STARTTLS.
Sending cold email through Postmark
Set by your Postmark plan. Use your Server API Token as both the SMTP username and the password.
Those caps make single-mailbox sending fine for personal mail but a poor fit for cold outreach at volume. Emailchaser spreads sending across warmed inboxes and manages deliverability, so you can scale without burning Postmark accounts.
Other smtp sending services
Setting up more than one mailbox? These sit in the same category as Postmark.
Common questions about Postmark SMTP settings
What are Postmark's SMTP settings?
Postmark's outgoing (SMTP) server is smtp.postmarkapp.com. Use port 587 (STARTTLS). STARTTLS on 587 (recommended), 2525 or 25. Postmark does not offer SSL/TLS on 465. Sign in with the SMTP credentials Postmark issues you, not a mailbox address and password.
What is Postmark's IMAP or POP3 server?
Postmark is a send-only service, so it has no IMAP or POP3 inbox. You configure it as an outgoing SMTP server only.
Which port should I use for Postmark?
Use port 587 with STARTTLS wherever it's offered, it's the modern standard for authenticated sending. Port 465 with SSL/TLS is a solid alternative. Avoid port 25, which most networks block for client sending. Postmark's recommended value is above.
Why won't my Postmark SMTP connection work?
Check authentication first: Use your Server API Token as both the SMTP username and the password. Find the token under your Postmark server > API Tokens, or create a dedicated SMTP token per message stream. Then confirm the host, port and security method match exactly, a 587/SSL or 465/STARTTLS mismatch will fail to connect.
Can I send bulk or cold email through Postmark?
Not at scale. Set by your Postmark plan. Providers throttle bursts to fight spam, so pushing cold email through one mailbox hits limits and wrecks deliverability. High-volume outreach belongs on dedicated infrastructure that spreads sending across warmed inboxes, which is what Emailchaser does.
Why does port 465 never work with Postmark?
Postmark only listens on ports 25, 2525 and 587, and it encrypts through the STARTTLS extension. There is no implicit SSL endpoint, so a client set to SSL on 465 will sit there until it times out. Pick 587 and set the security option to STARTTLS or TLS, not SSL.
Can I send marketing email through Postmark?
Bulk and marketing mail belongs on a broadcast message stream, which uses a different host, smtp-broadcasts.postmarkapp.com. The default outbound stream is for transactional mail such as receipts and password resets. Postmark reviews accounts on signup partly to keep the two apart.
Why can my new account only email my own domain?
Every Postmark account is reviewed by a person before it is opened up, normally in under 24 hours on a weekday. While you wait you can send to any domain you have added and confirmed, use the API, build templates and test webhooks. Their sink address test@blackhole.postmarkapp.com also accepts test mail.
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