I just tested the functionality of the “Alerts Recipient” option in 4 different websites, each one with 6 different email addresses, and all of them received the messages as expected.
[…] only the primary admin account ever receives the alerts
This is good, this tells us the feature is working.
The plugin doesn’t sends the mails by itself, it passes them to WordPress using a library that it comes bundled with called PHPMailer [1], then WordPress executes some filters and sends the mails.
The plugin stores all the email addresses in the same variable, so there is only two outcomes: either the operation succeeds for all the emails or fails for all of them.
Because you are receiving the alerts in at least one inbox, we can assume that the other emails are also receiving the alert, but the message is being blocked by something outside of the scope of the plugin, maybe their corresponding mail provider, another plugin, or your own server.
Troubleshooting and Possible Solution
Take one of the alerts that you’ve received in your admin account. Inspect the source code of the email and/or the headers, here is a step-by-step on how to do it on Gmail [2]. The “To” field should contain the list of all the emails that the plugin is sending the alerts to, then…
- If you can see more than one email in the “To” field, it means the feature works but the mail provider of the other emails is blocking the message.
- If you can see only one email in the “To” field, it means the plugin didn’t save the emails that you wanted to add to the list. You can fix this by granting write permissions to this file [3].
Let me know if you need more information.
[1] https://codex.www.ads-software.com/Plugin_API/Action_Reference/phpmailer_init
[2] https://support.google.com/mail/answer/29436
[3] /wp-content/uploads/sucuri/sucuri-settings.php
