1) No, my server has no Open relay... I'm tested in in many web pages (for example: http://www.abuse.net/relay.html
) and with scripts. This is not the cause.
2) In log file there is no info about users who sent e-mail. Log files look as I post it in root post.
3) I'm used this link and create logins from web forms... Only 1 client have mail form in his web application and it is secured by Secure code... and I thin - this is not the cause.