Status "success" but no mail is sent

[SarahDelCastillo]

Hello,

I'm trying to send mail to a single user from a Firebase cloud function, nothing fancy.
When I run the code locally on my computer the email is sent.
But when the same code is run by Firebase, despite this response:

{
  "Messages":[
    {
        "Status": "success", "CustomID": "", .....
    }
  ]
}

no mail arrives to the recipient, and nothing appears on the dashboard. There's no error whatsoever, I can't find the issue.
It's surprising since the exact same code works perfectly when run "manually".

[SarahDelCastillo]

I found out that the issue in my case was that I was using the wrong API keys, meaning that the sender email was not a valid one.
It would be great if the API told us that instead of just returning "success"