Default SMTP functionality if one of multiple addresses is invalid

Although this is effectively a programming question, my gut feeling is that subject is more suited to this site. However, if you feel it is better suited to Stackoverflow, please let me know and I’ll ask it there instead.

Is there default functionality (or recognised standards) across SMTP relays as how they deal with a single email that has multiple addresses, where one or more of the address is invalid?

In my testing it appears that if the SMTP detects an invalid address (normally because there is no corresponding address in the corporate SMTP system I’m connecting to) then the entire email fails – nobody on the email receives it.

Can anybody confirm if this is standard functionality?

Or is it something that can be configured at an individual SMTP level?

Or is it down to the individual SMTP vendor to decide how it deals with emails where one or more addresses are invalid?

Is it ever possible that the "other" recipients would still get the email?

Notes…

• I am a programmer, not a network administrator, so I have literally no experience of setting up or configuring SMTP relays. But I need to know how to handle those errors in my code should the SMTP I’m connected to come back with an issue.
• This is not specific to a particular SMTP vendor, as my application must run against any SMTP relay that our client desires.