My nlog config

appsettings.json

{
  // https://github.com/NLog/NLog.Extensions.Logging/wiki/NLog-configuration-with-appsettings.json
  "NLog": {
    "autoReload": true,
    "throwConfigExceptions": true,
    "extensions": [
      {
        "assembly": "NLog.Extensions.Logging"
      },
      {
        "assembly": "NLog.Web.AspNetCore"
      }
    ],
    "variables": {
      // in Azure App Service the logging base-directory should be D:\home\LogFiles
      "LOG_PATH": "${environment:LOG_PATH:whenEmpty=${basedir:fixtempdir=true}}"
    },
    "targets": {
      "async": true,
      "trace": {
        "type": "Trace"
      },
      "console": {
        "type": "ColoredConsole"
      },
      "file": {
        // https://github.com/nlog/NLog/wiki/File-target
        "type": "File",
        "layout": "${longdate}|${level:uppercase=true}|${logger}|${message}${onexception:|${exception:maxInnerExceptionLevel=5}}",
        "encoding": "utf-8",
        "fileName": "${var:LOG_PATH}/log.txt",
        "archiveFileName": "${var:LOG_PATH}/${date:format=yyyy-MM}/log.{#}.txt",
        "archiveEvery": "Day",
        "archiveNumbering": "Date",
        "archiveDateFormat": "yyyy-MM-dd",
        "maxArchiveDays": 90,
        "keepFileOpen": true,
        "concurrentWrites": false,
        "openFileCacheTimeout": 30
      },
      "mail": {
        // https://github.com/NLog/NLog/wiki/LimitingWrapper-target
        "type": "LimitingWrapper",
        "interval": "01:00",
        "messageLimit": 5,
        "target": {
          // https://github.com/NLog/NLog/wiki/Mail-target
          "type": "Mail",
          "smtpServer": "${environment:SMTP_HOST:whenEmpty=smtp.sendgrid.net}",
          "smtpPort": 587,
          "smtpAuthentication": "Basic",
          "smtpUserName": "${environment:SMTP_USER:whenEmpty=apikey}",
          "smtpPassword": "${environment:SMTP_PASS:whenEmpty=${environment:SENDGRID_API_KEY}}",
          "from": "${environment:LOG_MAIL_FROMNAME} <${environment:LOG_MAIL_FROM}>",
          "to": "${environment:LOG_MAIL_TO}",
          "subject": "Error Notification from ${environment:LOG_HOSTNAME:whenEmpty=${hostname}}",
          "body": "${longdate}|${logger}|${message}${newline}${exception:maxInnerExceptionLevel=5}",
          "addNewLines": true,
          "priority": "High"
        }
      }
    },
    // https://github.com/nlog/NLog/wiki/Configuration-file#rules
    "rules": {
      "1": {
        // Output hosting lifetime messages to console target for faster startup detection
        "logger": "Microsoft.Hosting.Lifetime",
        "minLevel": "Info",
        "writeTo": "console",
        "final": true
      },
      // Skip non-critical logs (BlackHole)
      "2": {
        "logger": "Microsoft.*",
        "maxLevel": "Info",
        "final": true
      },
      // log level: Trace|Debug|Info|Warn|Error|Fatal
      "3": {
        "logger": "*",
        "minLevel": "Trace",
        "writeTo": "trace"
      },
      "4": {
        "logger": "*",
        "minLevel": "Info",
        "writeTo": "file",
        "enabled": false
      },
      "5": {
        "logger": "*",
        "minLevel": "Error",
        "writeTo": "mail",
        "enabled": false
      }
    }
  }
}

nlog.config

<?xml version="1.0" encoding="utf-8" ?>
<!-- https://nlog-project.org/config/ -->
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      throwConfigExceptions="true">
  <extensions>
    <add assembly="NLog.Extensions.Logging" />
    <add assembly="NLog.Web.AspNetCore" />
  </extensions>
  <!-- in Azure App Service the logging base-directory should be D:\home\LogFiles -->
  <variable name="LOG_PATH" value="${environment:LOG_PATH:whenEmpty=${basedir:fixtempdir=true}}" />
  <targets async="true">
    <target name="trace" xsi:type="Trace" />
    <target name="console" xsi:type="ColoredConsole" />
    <!-- https://github.com/nlog/NLog/wiki/File-target -->
    <target name="file" xsi:type="File"
            layout="${longdate}|${level:uppercase=true}|${logger}|${message}${onexception:|${exception:maxInnerExceptionLevel=5}}"
            encoding="utf-8"
            fileName="${var:LOG_PATH}/log.txt"
            archiveFileName="${var:LOG_PATH}/${date:format=yyyy-MM}/log.{#}.txt"
            archiveEvery="Day"
            archiveNumbering="Date"
            archiveDateFormat="yyyy-MM-dd"
            maxArchiveDays="90"
            keepFileOpen="true" concurrentWrites="false" openFileCacheTimeout="30" />
    <!-- https://github.com/NLog/NLog/wiki/LimitingWrapper-target -->
    <target name="mail" xsi:type="LimitingWrapper" messageLimit="5" interval="01:00">
      <!-- https://github.com/NLog/NLog/wiki/Mail-target -->
        <target xsi:type="Mail"
              smtpServer="${environment:SMTP_HOST:whenEmpty=smtp.sendgrid.net}"
              smtpPort="587" smtpAuthentication="Basic"
              smtpUserName="${environment:SMTP_USER:whenEmpty=apikey}"
              smtpPassword="${environment:SMTP_PASS:whenEmpty=${environment:SENDGRID_API_KEY}}"
              from="${environment:LOG_MAIL_FROMNAME} &lt;${environment:LOG_MAIL_FROM}&gt;"
              to="${environment:LOG_MAIL_TO}"
              subject="Error Notification from ${environment:LOG_HOSTNAME:whenEmpty=${hostname}}"
              body="${longdate}|${logger}|${message}${newline}${exception:maxInnerExceptionLevel=5}"
              addNewLines="true"
              priority="High" />
    </target>
  </targets>
  <!-- https://github.com/nlog/NLog/wiki/Configuration-file#rules -->
  <rules>
    <!-- Output hosting lifetime messages to console target for faster startup detection -->
    <logger name="Microsoft.Hosting.Lifetime" minlevel="Info" writeTo="console" final="true" />
    
    <!-- Skip non-critical logs (BlackHole) -->
    <logger name="Microsoft.*" maxlevel="Info" final="true" />

    <!-- log level: Trace|Debug|Info|Warn|Error|Fatal -->
    <logger name="*" minlevel="Trace" writeTo="trace" />
    <logger name="*" minlevel="Info" writeTo="file" enabled="false" />
    <logger name="*" minlevel="Error" writeTo="mail" enabled="false" />
  </rules>
</nlog>