Debug Powermail
With TypoScript it's possible to enable some debug logging, which could help you to fix problems or a misconfiguration.
The logging output will not be saved by default. You need to enable it (see example below). https://docs.typo3.org/m/typo3/reference-coreapi/master/en-us/ApiOverview/Logging/Index.html
Comprehensive Example
plugin.tx_powermail.settings.setup {
    debug {
        settings = 0
        variables = 0
        mail = 0
        saveToTable = 0
        spamshield = 0
    }
}
        
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$GLOBALS['TYPO3_CONF_VARS']['LOG']['In2code']['Powermail']['writerConfiguration'] = [
  // configuration for WARNING severity, including all
  // levels with higher severity (ERROR, CRITICAL, EMERGENCY)
  \TYPO3\CMS\Core\Log\LogLevel::DEBUG => [
  // add a SyslogWriter
     'TYPO3\\CMS\\Core\\Log\\Writer\\FileWriter' => [
        'logFile' => 'typo3temp/logs/powermail.log',
     ],
  ],
];
        
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Configuration
| Relative Typoscript path | Description | Type | Default value | 
|---|---|---|---|
| debug.settings | Show Settings from TypoScript, Flexform and Extension Manager | 0/1 | 0 | 
| debug.variables | Show submitted variables | 0/1 | 0 | 
| debug.mail | Show mail arrays | 0/1 | 0 | 
| debug.saveToTable | Show saveToTable array | 0/1 | 0 | 
| debug.spamshield | Show spamtest results | 0/1 | 0 |