Boy, I went down the rabbit hole on this one. I'll spare the list all the gory details, but for the sake of posterity I figured I'll try to close the loop on this thread.
To make a long story short: After failing to get the printer working with just regular lpr, I tried CUPS to no avail. Along the way, however, I discovered a Perl script in a Linux package available on Brother's website that ostensibly could have served as an input filter for lpr (called, somewhat obviously, `lpdfilter`). After a bit of searching, I found a related thread [1] on a FreeBSD list and made some edits to this script, hoping that it would be the trick. Where I hit a wall was with a binary (also included in the package) called `rawtobr3`, that the Perl script expected. It appears to be proprietary Brother stuff and kept throwing an error, probably because it was built for Linux and not BSD. I did find a GitHub repo via a FreeBSD forum thread [2] that seemed to include _some_ version of this program, but it threw another error and the filter did not work. So, to wrap up: I do not recommend the Brother HLL2350DW for your OpenBSD printing needs. I may end up heeding the suggestions to simply buy a printer that speaks PostScript. Recommendations welcome. - Ben [1] https://lists.freebsd.org/pipermail/freebsd-questions/2017-July/277994.html [2] https://forums.freebsd.org/threads/port-for-brother-printer-drivers.78393/
