UPDATE: BPS Pro 13+ and BPS 2.0+ versions have a feature called: Setup Wizard AutoFix (AutoWhitelist|AutoSetup|AutoCleanup) that automatically creates plugin and theme whitelist rules and automatically sets up and cleans up caching plugins htaccess code.
https://wordpress.org/support/topic/test-email-settings-not-working-with-bulletproof-security/
The following button has never worked for me: WP-admin’s Events > Settings > Emails > Email Settings > Test Email Settings. After clicking it shows “Checking…” for about a second before reverting back to original text at the same time as “Server Error” appears right below the button in red text. The email does not come through and no other message is displayed.
Curiously, all the other emails except the test email do come through, which is why I remember reporting this only once some years ago but haven’t followed up before this. The issue occurs only with this AJAX-based test.
Solution:
1. Copy the wp-admin htaccess code below into this BPS wp-admin Custom Code text box: 3. CUSTOM CODE WPADMIN PLUGIN/FILE SKIP RULES
2. Click the save wp-admin Custom Code button.
3. Go to the Security Modes page and click the wp-admin folder BulletProof Mode Activate button.
# admin-ajax.php skip/bypass rule
RewriteCond %{REQUEST_URI} (admin-ajax\.php) [NC]
RewriteRule . - [S=2]
.
