Paul,
You can use SECURITY > ADVANCED SETTINGS > SMTP BLOCKING to block based upon EHLO DOMAIN. Although you can block based upon a specific EHLO Domain it does also allow for Wildcards in the EHLO Domain. We do this all the time for some Spambot Networks that use predictable names for their EHLO (i.e., prs.*.link, res.*.us, wer*.*.work, iax*.*.ninja, etc). Although there may be hundreds or thousands of different ELHOs for one of these wildcard domains, they all get stopped by SmarterMail.
Unfortunately, there is no way inherent in SmarterMail to parse out EHLO for Spammers. You just have to grep the SMTP Logs for EHLO addresses. I noticed that if I kept track of incoming connections for 90-day spans the repeat offenders and the patterns in their EHLO Domains was pretty obvious, enabling me to bulk block their entire botnets.