Provider guide · Mailjet
Mailjet authenticates WordPress with its API key pair, not with your dashboard login, and refuses any sender address you have not validated first. Both rules are simple; both produce cryptic errors when missed. Here is the short version.
1 · Credentials
Mailjet gives every account an API Key and a Secret Key, and SMTP borrows exactly that pair. Your dashboard email and password stay out of it.
In Mailjet, open your account menu, then the SMTP and SEND API settings page. It shows the server, the ports, and both keys.
It is public-ish and always visible.
Newer accounts display it once at creation. If it is lost, reset it from the API Key Management page, and remember every integration using the old secret stops at that moment.
Under Sender domains & addresses: either confirm a single address by email, or validate the whole domain and add the SPF and DKIM records Mailjet provides, the option that scales past one address.
2 · In the plugin
Selecting the Mailjet preset fills the server (in-v3.mailjet.com), the port (587) and the encryption (TLS). What remains is yours.
The API Key.
The Secret Key.
A validated sender address, or any address on a validated domain.
Save, then use Send Test Email. If authentication passes but the send is refused, the phrase to look for in the log is “relay access denied”, and it means the From address, not the credentials.
3 · Pitfalls
Mailjet’s errors are accurate once translated; these are the three worth knowing before they happen.
This error reads like an authentication failure, and it is not one. It is Mailjet declining to send from an address you never validated. Add the address, or its whole domain, under Sender domains & addresses, complete the validation, and the same configuration starts working without touching a credential.
The Secret Key is shared by everything that sends through your account. Reset it to fix one forgotten value and any other tool using the old secret starts failing at the same minute. Reset deliberately, then update WordPress and whatever else authenticates with it in one sitting.
Free accounts get about 200 emails a day within 6,000 a month, and Mailjet adds its logo to the footer of free-plan emails. Fine for trying it out; for a production shop, the daily cap and the branded footer are usually the two reasons to move to a paid tier. The plugin’s volume alerts can warn you as you approach the daily number.
The email log keeps the exact error message the server returned, which is the fastest route to the cause. The documentation walks through the common ones.
There is a guide like this one for each of the twelve presets, from Gmail to Amazon SES, and the plugin takes any other SMTP server too.