I'm sending email to different country using Tor Browser. Is there an advantage or disadvantage, specifing the Tor exit node be located in the country the email is addressed to?
Actually the exit node will connect to your email server (SMTP server) and sends your email. It depends on your SMTP security policies which can prevent a user who is constantly switch connection IP (exit node's IP). And more, I guess that you're using user+pass to authenticate yourself to SMTP server, therefore SMTP server knows who you are and whom the message in sent to and even Email content if the message is not encrypted. The only private thing is your real IP.
Another point, if your SMTP server does not use SSL/TLS for connection, the exit node will know your user name, password and email content (if is not encrypted).
You say Tor Browser so I assume that you mean web mail and not using an actual mail server.
Let's say you are using the onion service for ProtonMail. The advantage of using the onion service is that no one knows that you are using ProtonMail. Other than that, it doesn't matter.
Let's say you are using web mail from another provider. Because you are using Tor, they may block or even ban you for using Tor. After all, then can't see if you are a real person or a spammer. This is clearly a big disadvantage.
The best course of action, if you are technically saavy enough and can pay for it, is to run your own mail server and provide your onion web interface.
See also: sending email through .onion