I have a Linux server which uses Postfix for email. Its on a dynamic ip so I use the "relayhost" parameter to send outgoing mail through an ssh tunnel to another server on a static ip and from there it goes out to the real world. That's been working fine since about 1998 or so.
I'm currently developing some software for a client, and it sends email to various people in that client's organization based on information in a database. For my initial testing, I created fake people who all had email addresses like ptomblin+client1@{mydomain}.com, which worked fine and sent all the email to me. But now I'm working with a live database, and all the email addresses are for real people in the client's organization. I don't particularly want to send email to those people telling them that the system access they requested has been provisioned, so I'd like a way to redirect all email to that client's domain to either my email address or to a file.