Another suggestion would be PHPMailer. Its website comes complete with a list of example scripts as well. I've always chosen this class because it's quite versatile.
marcnyc;10942163 wrote:if I install a script and their function is thirdparty_mail() I should just be able to replace mail() with thirdparty_mail() as long as it takes the parameters in the same order... that's what I meant...
As dagon suggested, this is unlikely; whichever library you go with, you'll have to look at the documentation/code examples and learn how it's used.
If it were as simple as changing 'mail(' to 'newsoftware_mail(' then there wouldn't be such job titles as "Software Engineer" and whatnot since you could hire a 15-year-old to press Control+F, "mail(", "newsoftware_mail(", Replace All.