If someone's maintaining an old/obscure email client, I would expect them to be importing a TLS library under the "don't roll your own crypto" principle. Assuming it's been updated at some point in the last ~15 years, it's probably capable of auto-negotiating to something better than 3DES.

And if it hasn't been updated for that long, it probably doesn't support TLS 1.2 and is getting rejected from just about everything for that reason.