Problem with local domain senders

[nikira]

Hi All,
i have problem with my server zcs-5.0.11
unexisting user can send e-mail to me and i recieve it for example:

==============================================
telnet mail.mydomain.com 25
Trying mail.mydomain.com...
Connected to mail.mydomain.com.
Escape character is '^]'.
220 mail.mydomain.com ESMTP Postfix
ehlo mail.mydomain.com
250-mail.mydomain.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
mail from:blabla@mydomain.com
250 2.1.0 Ok
rcpt to:john@mydomain.com
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
subject:test123
ops
.
250 2.0.0 Ok: queued as 685DD134228
=================================================

i have user john@mydomain.com
but i don't have user blabla@mydomain.com
The ip from were i do the telnet is not relayed(i have relay only for localhost and server ip), also i set zimbra to ask for authentication without TLS.
In generaly server is not open relay because this problem is only for local domain, if i try to send to another domain it reject me.
Can i make some settings to check for valid sender from my domains, because i recieving many spams from nonexistent users in my domain for example "98d7fv987y@mydomain.com"
May be my question is stuped but i realy need help.

Thanks in advance

[phoenix]

Improving Anti-spam system - Zimbra :: Wiki

[nikira]

Thank you for this link, but my problem is mail from, because non existig user from my domain can send to my real user, for example rcpt to:non_existent@mydomain.com can send e-mail to john@mydomain.com, i realy have user john@mydomain.com but i don't have non_existent@mydomain.com.

[phoenix]

Can i make some settings to check for valid sender from my domains, because i recieving many spams from nonexistent users in my domain for example "98d7fv987y@mydomain.com"

This was your original question, the link I've given you is the answer to that question. Are you saying the problem is something different from that?