Sonic did some config change a week ago that made my outgoing email stop working. That's ok, I was doing it the wrong way anyway - I was trying to send mail directly, while Sonic wants customers to relay through their server for better spam protection. Fine. But when I tried setting up the relay, I had some trouble getting it to work, Sonic's server was rejecting my authentication. Turns out the problem is that stock FreeBSD sendmail is not compiled with the -DSASL option. That stands for "Simple Authentication and Security Layer" and it's necessary for any sort of authentication, even just sending a cleartext (over SSL) password. I thought at first I would have to build sendmail from source to set the option, but then learned there's a pkg version that includes SASL. Installed that, edited sendmail.mc / mailer.conf / rc.conf to use it, rebooted, and things seem to be working now. Yay!