Resend SMTP Settings
Developer-focused email service where the SMTP username is always the word resend.
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Outgoing mail (SMTP)
SMTP server
smtp.resend.com
Port. STARTTLS
587
Port. SSL/TLS
465
Security
SSL/TLS on 465 (recommended) or 2465, or STARTTLS on 587 or 2587.
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
100 emails per day on the free plan; higher on paid plans.
Authentication
Use the literal username "resend" and paste your API key (including the re_ prefix) as the password.
App password
Create the API key in the Resend dashboard under API Keys.
Resend is a send-only relay: there is no IMAP or POP inbox. It will not relay mail from a domain you have not verified.
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Resend SMTP, IMAP and POP3 settings
Resend is a newer service aimed at developers, and its SMTP login is blunt: the username is always the word resend and the password is an API key. Alongside the usual 25, 465 and 587 it also answers on 2465 and 2587 for hosts that block the standard ports. Until you verify a domain of your own, Resend will only let you email your own address.
Resend 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 Resend's own documentation: resend.com. Ports and limits change, so check there too if something will not connect.
Resend 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 Resend username and password
Wrong credentials, not a wrong port, are the usual reason a Resend connection fails. These are the exact values to type.
resend (the literal word, identical for every account)
How to set up Resend in a mail client
The exact path through Resend's own settings, in order.
- 1
Add and verify your domain
Go to https://resend.com/domains, click Add Domain, enter the name and publish the DNS records Resend shows. Skip this and you can only mail the address on your own account.
- 2
Create an API key
At https://resend.com/api-keys create a key. You can set its permission and scope it to a single domain when you create it or edit it later.
- 3
Fill in the relay settings
Host smtp.resend.com. Ports 25, 587 and 2587 use STARTTLS; ports 465 and 2465 use SSL from the first byte.
- 4
Type resend as the username
The username is the literal lower-case word resend for every account. Paste the API key into the password field.
- 5
Optional: add an idempotency key
Set the Resend-Idempotency-Key header on a message so a retry does not send it a second time. Custom headers such as List-Unsubscribe work over SMTP as well, if your client supports adding them.
What Resend looks like filled in
Every mail client asks for the same handful of fields. Here they are with Resend's values already in place.
Account settings: Resend
Server
smtp.resend.comPort
465Encryption
SSL/TLSAuthentication
RequiredUsername
resend (the literal word, identical for every account)Password
A Resend API key with sending permissionIMAP / POP3
Not applicable. Resend 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.
Resend SMTP settings in Thunderbird
The outgoing server dialog with Resend's details entered. Outlook and Apple Mail ask for the same four things under slightly different names.
Which port should you use for Resend?
SSL/TLS on 465 (recommended) or 2465, or STARTTLS on 587 or 2587.
STARTTLS
Starts as a plain connection, then upgrades to an encrypted one. The modern standard for sending.
SSL/TLS
Encrypted from the first byte. Widely supported and a good choice when 587 is blocked.
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 Resend connection is failing
The failures people actually hit with Resend, and what fixes each one.
You are sending from a resend.dev address, which is test-only. Add and verify your own domain at resend.com/domains, then change the From address to one on that domain.
Resend ignores your account email for SMTP. The username is the six letters resend, in lower case, for everyone.
Free accounts get 100 a day inside 3,000 a month. Watch out for the counting rule: every To, CC and BCC address counts as its own email against the quota.
Accounts start at 10 requests a second, and that limit applies per team across every API key rather than per key. Space the sends out or ask Resend to raise it.
The ceiling is 40 MB per email measured after base64 encoding, so a file that is 30 MB on disk is already over the line.
Resend sending limits
Free plan is also capped at 3,000 a month, and the 10 requests a second rate limit is per team, shared across all API keys
Per day
100 emails a day on the free plan
Recipients per message
50 addresses in the To field
Max attachment
40 MB per email, measured after base64 encoding
Sending cold email through Resend
100 emails per day on the free plan; higher on paid plans. Use the literal username "resend" and paste your API key (including the re_ prefix) as 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 Resend accounts.
Other smtp sending services
Setting up more than one mailbox? These sit in the same category as Resend.
Common questions about Resend SMTP settings
What are Resend's SMTP settings?
Resend's outgoing (SMTP) server is smtp.resend.com. Use port 587 (STARTTLS) or 465 (SSL/TLS). SSL/TLS on 465 (recommended) or 2465, or STARTTLS on 587 or 2587. Sign in with the SMTP credentials Resend issues you, not a mailbox address and password.
What is Resend's IMAP or POP3 server?
Resend 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 Resend?
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. Resend's recommended value is above.
Why won't my Resend SMTP connection work?
Check authentication first: Use the literal username "resend" and paste your API key (including the re_ prefix) as the password. Create the API key in the Resend dashboard under API Keys. 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 Resend?
Not at scale. 100 emails per day on the free plan; higher on paid plans. 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.
What username does Resend's SMTP server want?
The word resend, in lower case, and nothing else. It is the same string for every customer, which surprises people used to relays that want an email address or an account ID. Your identity comes from the API key you send as the password.
Why can I only email myself?
You are sending from the shared resend.dev domain, which Resend restricts to testing. It will only deliver to the address attached to your Resend account, and anything else comes back as a 403 naming your own address. Verifying your own domain at resend.com/domains removes the restriction.
Are the SMTP limits different from the API limits?
No. Resend's documentation says the rate limit for SMTP is the same as the API, so the same 10 requests a second per team and the same daily and monthly quotas apply whichever route you use. There is no separate SMTP allowance to configure.
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