SmtpCommandException when sending mails

Oh, in addition, we're using version 9.2.

Did you set the SMTP Relay Parameter? 

Can you post the parameters of the failed sendmail job?

Yes, I set it, in fact the string "<SMTP Relay>" that I inserted in the error was just a placholder to the real value of the parameter.

The parameters are:
- AcceptSelfSignedCert: ""
- Account: ""
- Address: "user.test@domain.com"
- AllowServerNameMismatchInCert: ""
- AuthenticationString: long encrypted string
- BaseObject: "<Patch Display="Test, User (USTE)"><Key> etc. etc. "
- ConnectionProvider: "VI.DB.ViSqlFactory,VI.DB"
- ConnectionString: long encrypted string
- Domain: ""
- Encrypt: ""
- EncryptionCertificateScript: ""
- MailID: "CCC - Employee - End date has changed"
- Password: long encrypted string
- SenderAddress: mail of the sender
- Sign: False
- SignCertificateThumbprint: ""
- SmtpPort: 25
- SmtpServer: name of the SMTP Server
- TransportSecurity: "None"
- UseDefaultCredentials: "False"

I would try a connection to that MTA using simple smtp commands , or either an external email client, and try to send mails via that MTA, so you could discard , isolate and locate the origin of the problem: SMTP server (MTA) or OneIdentity.

Seems to me (as the error message offers no other info) the server is refusing to relay mail depending on the sender/recipient domain or ip address (mta based problem).

Hello,

at last it was a server issue. Unfortunately I don't know which issue. The customer just gave me another server and that worked.

Thank you everyone for the help,
Lucrezia

Hello,

at last it was a server issue. Unfortunately I don't know which issue. The customer just gave me another server and that worked.

Thank you everyone for the help,
Lucrezia