hMailserver

hMailServer is a free and open source mail server.

To add hMailserver SMTP and IMAP protection, add this block to the config file:

      <!-- hMailserver failed logins, Windows, at least SMTP or POP3 ord IMAP logs must be turned on! -->
      <LogFile>
        <Source>hMailserver</Source>
        <PathAndMask>
          C:/Program Files/hMailserver/logs/**/*.log
          C:/Program Files (x86)/hMailserver/logs/**/*.log
        </PathAndMask>
        <FailedLoginRegex>
          <![CDATA[
            ^".*\t.*\t.*\t"(?<timestamp>.+)"\t"(?<ipaddress>.+)"\t.*(?:Authentication failed|Invalid user name or password).*$
          ]]>
        </FailedLoginRegex>
        <FailedLoginRegexTimestampFormat>yyyy-MM-dd HH:mm:ss.fff</FailedLoginRegexTimestampFormat>
        <PlatformRegex>Windows</PlatformRegex>
        <PingInterval>10000</PingInterval>
        <MaxFileSize>16777216</MaxFileSize>
      </LogFile>

To get this working you must activate SMTP and IMAP logging in the admin interface of hMailserver. There are hidden options to reduce the logging verbosity via the server's .ini file: hMailserver official forum

You may want to use LogLevel=1 (lowest) together with MaxLogLineLen=250. It still includes the failed logins and truncates the IMAP log lines to 250 characters per line.