I know it is a vague question, but maybe it is a common problem. Anyone used

email.send

and NS showed that the email was sent, while it actually wasn't?

@Marwan Are you in a sandbox or development environment?

No

Will check that, thanks very much.

Are you sure it wasn't actually sent? If so, how do you know. For example, NS might have sent it, but your email system might have rejected it (this is different from going to spam). I'd suggest setting up DKIM, SPF and DMARC to avoid this issue. https://system.netsuite.com/app/help/helpcenter.nl?fid=book_1556559731.html

In Setup>Email Preferences You can BCC all NetSuite generated email while testing. Handy way to see what actually goes out to the interweb

@Lee Hopper You were right, the server was the problem. Thanks very much @Netsuite Tragic ❤️