PHP has a mail() function, which in a standard LAMP stack production environment calls *nix sendmail, or perhaps postfix. XAMPP for Windows supports PHP's mail() by pointing it to a copy of Byron Jones' public-licensed "fake sendmail for Windows", in theory providing cross-platform portability for PHP apps that rely on mail().

I forget what the sticking point was, but when I broke into web dev I had difficulties with XAMPP's implementation, and turned instead to Martin Lambers' msmtp. My solution was to rename the Windows binary to sendmail.exe and replace XAMPP's (Jones') sendmail with Lambers'.

I downloaded the latest mSMTP.exe, v1.4.30, and dropped it on top of ghost's dev sendmail.exe - but it didn't function as expected. So I backed up a step: zipped up the contents of shadow's xampp/sendmail folder with the 1.4.19 version of mSMTP, an .ini file, a .log file, and a couple of DLLs (libeay32.dll and ssleay32.dll), recycled-binned ghost's xampp/sendmail folder, and reconstituted shadow's on ghost. Now my test app worked.

So THEN I twiddled just the mSMTP executable, rolling forward to v1.4.30 and hoping it wasn't linked against incompatible DLLs. Poked my test app again and sure enough, no relay. So apparently I'm stuck using an older mSMTP; but at least I have a roll-up of known-working executable and DLLs in softlib/mSMTP.