Send WordPress 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 WordPress straight away; if you lose it, rotate the credential.

The From address in WordPress 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.

WordPress has no SMTP settings of its own, so you add them with a plugin. Both plugins below have a generic Other SMTP option; pick one.

WP Mail SMTP: the Other SMTP mailer

In the WordPress admin, open WP Mail SMTP, Settings, the General tab:

TLS is the right encryption for port 587: in WP Mail SMTP, TLS means STARTTLS and SSL means TLS on connect. Force From Email matters here, because it stops other plugins from sending as an address that is not on your verified domain, which the relay would refuse.

Or keep the password out of the database

WP Mail SMTP also reads its settings from constants in wp-config.php, which keeps the password out of the admin screen and the database:

define( 'WPMS_ON', true );
define( 'WPMS_MAILER', 'smtp' );
define( 'WPMS_SMTP_HOST', 'smtp.ackuna.com' );
define( 'WPMS_SMTP_PORT', 587 );
define( 'WPMS_SSL', 'tls' );
define( 'WPMS_SMTP_AUTOTLS', true );
define( 'WPMS_SMTP_AUTH', true );
define( 'WPMS_SMTP_USER', 'YOUR_SMTP_USERNAME' );
define( 'WPMS_SMTP_PASS', 'YOUR_SMTP_PASSWORD' );
define( 'WPMS_MAIL_FROM', '[email protected]' );
define( 'WPMS_MAIL_FROM_FORCE', true );
define( 'WPMS_MAIL_FROM_NAME', 'Your Site' );

The plugin's own comment on WPMS_SSL reads: "'ssl' is implicit TLS, 'tls' is STARTTLS". smtp is the plugin's internal name for the Other SMTP mailer.

FluentSMTP: the Other SMTP connection

In the WordPress admin, open Settings, FluentSMTP, Add Connection (or the first-run wizard) and choose Other SMTP:

FluentSMTP's docs pair the encryption with the port the same way: SSL on 465, TLS on 25 or 587. Click Save Connection Settings.

Send a test email

• WP Mail SMTP: open WP Mail SMTP, Tools, the Email Test tab, enter your address in Send To and click Send Email.
• FluentSMTP: click Send Test Email in the plugin's top bar.

A success message means the relay accepted the message. It is also listed 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 WordPress 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.