Where are these "extra" RCPT_TO lines coming from when I send an email via SSMTP?

I've been using SSTMP on a local FreeBSD machine to send stuff like the output of certain cron jobs to my "real" main email account, which is not hosted on the same machine (or even domain). For example, I have a daily cron job set up as so:

smartctl -a /dev/ada0 | grep overall-health | mail -s "Silicon daily smartctl" bob@vesterman.com

This works fine, insofar as the mail being successfully delivered to my "real" email account. However, every time I send a message, I also receive a bunch of warning and bounce messages from my "real" email account's mail system. I found that `mail has a "verbose" flag, -v`, which shows the conversation between my SSMTP and the host of my "real" email account. I tried it out, and noticed the following interesting portion:

[->] RCPT TO:
[] RCPT TO:
[] RCPT TO:
[] RCPT TO:
[] RCPT TO:
[<-] 250 Accepted

So SSMTP is saying that the message should be sent not only to the intended recipient, but also to three other addresses? And one of them is especially weird looking ("/usr/local/sbin/ssmtp@vesterman.com"), and for some reason that one gets *two* RCPT TO lines. I have no idea where these "extra" RCPT TO lines are coming from. Anyone have any idea? Thanks. Contents of my /usr/local/etc/ssmtp/ssmtp.conf:

root=bob@vesterman.com
mailhub=mail.vesterman.com:465
rewriteDomain=vesterman.com
hostname=silicon.vestertopia.net
FromLineOverride=YES
UseTLS=YES
AuthUser=robotsender@vesterman.com
AuthPass=hunter2