Send n8n email through SMTP with Ackuna

Before you start

You need three things from Ackuna. Each takes a few minutes, except the review in step 2.

1. An Ackuna account. Create one for free; no card is needed.
2. A verified sending domain. Add the domain your app sends from (for example yourdomain.com) under SMTP Relay, Domains in the console and publish the SPF, DKIM and DMARC records it shows you. The console checks them for you. A new sending domain is also reviewed by our team before it can send; that is not instant, and until it is approved the relay answers 452.
3. An SMTP credential for that domain. Under SMTP Relay, Credentials, create one for the verified domain. You get a username (smtp_…) and a password (sc_…). The password is shown once, so paste it into n8n straight away; if you lose it, rotate the credential.

The From address in n8n must be on exactly that domain. A credential for yourdomain.com can send as [email protected], but not from a subdomain such as mail.yourdomain.com or from another domain.

The Send Email node: an SMTP credential

In the Send Email node, under Credential to connect with, create a new SMTP account credential and fill it in:

The n8n docs say it directly: turn SSL/TLS off for port 587, because port 587 uses STARTTLS. Leave Disable STARTTLS off as well; switching it on would stop the upgrade and the relay would refuse the login.

In the Send Email node itself, set From Email to an address on your verified domain, such as [email protected].

Self-hosted n8n: invitation and password reset emails

n8n's own emails (inviting users, resetting passwords) use environment variables, not the node credential:

N8N_EMAIL_MODE=smtp
N8N_SMTP_HOST=smtp.ackuna.com
N8N_SMTP_PORT=587
N8N_SMTP_USER=YOUR_SMTP_USERNAME
N8N_SMTP_PASS=YOUR_SMTP_PASSWORD
N8N_SMTP_SENDER="Your App <[email protected]>"
N8N_SMTP_SSL=false
N8N_SMTP_STARTTLS=true

N8N_SMTP_SSL defaults to true in n8n, which means TLS on connect. That does not work on port 587, so set it to false explicitly and keep N8N_SMTP_STARTTLS=true. Restart n8n after changing the variables.

Send a test email

For the node: add a Send Email node with the new credential to a workflow, put your own address in To Email, and execute the node. For the user-management emails: invite a user at an address you can read. Both show up under SMTP Relay, Messages in the Ackuna console.

Common errors

Authentication failed (535)

The username or password is wrong, the credential was revoked, or its domain is no longer active. Copy both values again from the console, with no spaces around them. If you no longer have the password, rotate the credential and paste the new one.

TLS handshake error, "wrong version number" or a connection that hangs

The app is trying SSL/TLS on connect, which the relay does not offer. Use port 587 with STARTTLS: the connection starts in plain text and is upgraded before the login. If the connection times out instead, check that your host or firewall allows outgoing connections to port 587; some cloud providers block it on new servers until you ask them to lift the block.

Sender rejected (550)

The From address is not on the domain the credential was created for. Set the From address in n8n to an address on that exact domain. The same code is used for a recipient on your suppression list, because an earlier message to them bounced or was marked as spam.

Temporarily rejected (452)

Either you have reached your daily or monthly limit, or the sending domain is still waiting for review. Both are temporary: a mail server retries later, and the console shows your usage. A message with more than 10 recipients is also refused with 452, and one over 10 MB with 552.

Mail that is accepted but lands in spam usually points at DNS, not SMTP. Run the Email DNS check on your domain, or the SPF, DKIM and DMARC checkers one by one.

Limits

• The Free plan includes 3,000 relay emails a month and 100 a day, 1 SMTP credential and 1 sending domain. Paid plans and their limits are on the pricing page.
• New accounts start on lower limits until Ackuna has reviewed them: at most 20 Agent Mail, 200 SMTP relay and 500 newsletter emails a day, whatever the plan allows. After the review the plan limits above apply.
• Each new sending domain is reviewed before it can send.
• One message can have up to 10 recipients and be up to 10 MB.
• While we deploy an update, port 587 stays open and the relay holds the mail it accepts, then sends it when the update is done. A login it cannot check during that time gets a temporary 451; a retry goes through once the update is done.