Support » Plugin: MailerSend - Official SMTP Integration » Could not authenticate.

  • Two of the other SMTP plugins in the repository work absolutely fine with the same credentials, but all I can get from this plugin is “wp_mail_failed – SMTP Error: Could not authenticate.”

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  • Plugin Author MailerSend


    Hi Terrence,
    I’m Agathe, MailerSend’s project manager.

    We’re sorry to hear you’ve encountered an error while attempting to send via SMTP. I haven’t been able to find your account, would you mind sending an email to so we can check?

    We recommend you run through some troubleshooting steps to resolve this as usually this type of problem can happen for the following reasons:

    Wrong username or password: these fields are both case-sensitive, so you need to make sure both are exactly as shown in your account and that your provider is not changing them to lowercase or uppercase.

    Sender email address: ensure the ‘from’ address you have opted to use matches the domain you’ve verified in your MailerSend account and is entered in lowercase.

    Security settings: if you are testing MailerSend’s SMTP using a local client, you’ll need to make sure you do not have a firewall blocking the connection. You might find you need to set your firewall software to allow SMTP sending using port 587.

    I hope that helps, but please feel free to let us know if you continue to have problems.


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