Unable to configure mail for Elmah
<configSections>
    <sectionGroup name="elmah">
      <section name="security" requirePermission="false" type="Elmah.SecuritySectionHandler, Elmah" />
      <section name="errorLog" requirePermission="false" type="Elmah.ErrorLogSectionHandler, Elmah" />
      <section name="errorMail" requirePermission="false" type="Elmah.ErrorMailSectionHandler, Elmah" />
      <section name="errorFilter" requirePermission="false" type="Elmah.ErrorFilterSectionHandler, Elmah" />
    </sectionGroup>
  </configSections>
 <mailSettings>
      <smtp deliveryMethod="Network">
        <network host="smtp.gmail.com"
           port="587"
           userName="example@gmail.com"
           password="password" />
        </smtp>
      </mailSettings>
  </system.net>
 <elmah>
    <errorMail
              from="example1@gmail.com"
              to="example2@gmail.com"
              sync="true"
              smtpPort="0"
              useSsl="true"
            />
  </elmah>

<?xml version="1.0"?>
<configuration>
    <configSections>
        <!--ELMAH-->
        <sectionGroup name="elmah">
            <section name="security" requirePermission="false" type="Elmah.SecuritySectionHandler, Elmah"/>
            <section name="errorLog" requirePermission="false" type="Elmah.ErrorLogSectionHandler, Elmah"/>
            <section name="errorMail" requirePermission="false" type="Elmah.ErrorMailSectionHandler, Elmah"/>
            <section name="errorFilter" requirePermission="false" type="Elmah.ErrorFilterSectionHandler, Elmah"/>
        </sectionGroup>
    </configSections>
    <elmah>
        <security allowRemoteAccess="1"/>
        <!-- set the smtpPort attribute to "0". Doing so will cause ELMAH to use the port defined per the <system.net> settings -->
        <errorMail from="example1@gmail.com" to="example2@gmail.com" subject="ERROR(test):" async="false" smtpPort="0" useSsl="true" />
    </elmah>
    <!--System.net Mail setup-->
    <system.net>
        <mailSettings>
            <smtp deliveryMethod="network">
                <network host="smtp.gmail.com" port="587" userName="example1@gmail.com" password="..." />
            </smtp>
        </mailSettings>
    </system.net>
    <appSettings>
    ...
 </appSettings>
    <connectionStrings>
        ...
    </connectionStrings>
    <system.web>
        <compilation debug="true">
            <assemblies>
                ...
        </compilation>
        <customErrors mode="Off"/>
        ...
        <httpHandlers>
            ...
            <!--ELMAH-->
            <add verb="POST,GET,HEAD" path="MyErrorPage/elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah"/>
        </httpHandlers>
        <httpModules>
            ...
            <!-- ELMAH: Logging module -->
            <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah"/>
            <!-- <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah"/> -->
            <!--<add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah"/>-->
        </httpModules>
        <httpRuntime maxRequestLength="458292"/>
        <authentication mode="Forms">
            ...
        </authentication>
    ...
    </system.web>
    <location path="MyErrorPage.aspx">
        <system.web>
            <authorization>
                <allow users="?"/>
            </authorization>
        </system.web>
    </location>
    <!--
        The system.webServer section is required for running ASP.NET AJAX under Internet
        Information Services 7.0.  It is not necessary for previous version of IIS.
    -->
    <system.webServer>
        <validation validateIntegratedModeConfiguration="false"/>
        <modules runAllManagedModulesForAllRequests="true">
            ...
            <!-- ELMAH-->
            <add name="ErrorLog" type="Elmah.ErrorLogModule, Elmah"/>
            <add name="ErrorMail" type="Elmah.ErrorMailModule, Elmah"/>
            <add name="ErrorFilter" type="Elmah.ErrorFilterModule, Elmah"/>
        </modules>
        <handlers>
            ...
            <!--ELMAH-->
            <add name="Elmah" verb="POST,GET,HEAD" path="MyErrorPage/elmah.axd" type="Elmah.ErrorLogPageFactory, Elmah"/>
        </handlers>
    </system.webServer>
    <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            ...
        </assemblyBinding>
    </runtime>
    <location path="MyErrorPage/elmah.axd">
        <system.web>
      <authorization>
        <deny users="?"/>
        <allow users="?"/>
      </authorization>
        </system.web>
    </location>
</configuration>

<system.net>
    <mailSettings>
      <smtp deliveryMethod="Network">
        <network host="smtp.gmail.com" defaultCredentials="false"
        port="587" userName ="yourMailId@gmail.com" password="yourMailPassword" />
      </smtp>
    </mailSettings>
   </system.net>