You can send email direct to an IP address... maybe. There is nothing needed client side, success depends on how the server is configured.
For example on my mail server, the domain in the destination (an IP in your use case) is checked against the contents of a mysql db table, and if it is in that table the mail is accepted and added to the que for delivery processing.
A very basic set up though for a mail server would NOT run such a check and instead simply accept the message and apply its delivery rules.
So definitely maybe.
As to doing something like modifying your
hosts file to give a name to your IP address or to point a "real" name to some other IP address, while that works with web browsers, game consoles, etc. it doesn't work with email. The sending mail server uses DNS to look up a
MX Record for the destination domain/IP, not your local computer.