Ref: http://www.winvistatips.com/security-log-eventid-529-smtp-t673781.html
Ref: http://www.pcreview.co.uk/forums/thread-1596278.php
Bad guys are trying to authenticate server via port 25.
How to reproduce this log:
# Type telnet
# Type EHLO
# Type AUTH LOGIN. The server responds with an encrypted prompt for your user name.
# Enter your user name encrypted in base 64. You can use one of several tools that are available to encode your user name.
# The server responds with an encrypted base 64 prompt for your password. Enter your password encrypted in base 64.
# Type MAIL FROM:
# Type RCPT TO:
# Type DATA.
Or by using hacking tools : Xscan
Solution: You can minimizing the attack by enabling tar pitting
Ref : http://support.microsoft.com/kb/842851/en-us
I have been trying to figure out where this error has been coming from for weeks. Than you for this simple answer that no one else knew (or I could find).