Prefilled Default administrator email gives Test email has failed.

[ipajen]

Bug Report

Description

Prefilled Default administrator email gives Test email has failed.

Environment

• WordPress: 6.6.1
• PHP: 8.3.10
• Server: LiteSpeed
• Database: mysqli (Server: 10.6.18-MariaDB / Client: mysqlnd 8.3.10)
• Browser: Edge 127.0.0.0 (Windows 10/11)
• Theme: Twenty Twenty-Four 1.2
• MU-Plugins:
  • block-automation-by-installatron.php
  • Health Check Troubleshooting Mode 1.9.2
• Plugins:
  • Core Rollback 1.3.5
  • Health Check & Troubleshooting 1.7.1
  • Limit Login Attempts Reloaded 2.26.12
  • Plugin Check (PCP) 1.0.2
  • Query Monitor 3.16.4
  • Stop User Enumeration 1.6.1
  • WordPress Beta Tester 3.5.6
  • WPVulnerability 3.4.0

Steps to Reproduce

1. Don't enter any "Email addresses to notify", use the Default administrator email: for example: my@email.se
2. Go to Email test and click on "Send email" It shows that The mail will be sent from: my@email.se
3. 🐞 Bug occurs.

Expected Results

1. ✅ No error message and the default email should be used.

Actual Results

1. ❌ Error message "Test email has failed. Please, check your email settings." and Deprecated: explode(): Passing null to parameter #2 ($string) of type string is deprecated in \wp-includes\pluggable.php on line 225

Note: If entering the email adress in Email addresses to notify everything works fine.