1. Copy SmarterMail’s existing clamd.conf and freshclam.conf configuration files to ClamAV’s installation folder (C:\Program Files (x86)\SmarterTools\SmarterMail\Service\Clam\etc to C:\Program Files\ClamAV)
2. Update the configuration files as needed (mainly the database and log directories, and localhost port from 3310 to be able to verify your installation is being used)
3. Install clamd and freshclam’s Windows Services through the terminal and set them to Automatically start in Services.
4. In SmarterMail’s administrator area under Settings>Antivirus, change the port to the localhost port you chose above, and “ClamAV is on a remote server” (otherwise SmarterMail will use its own copy).
5. Try sending an email with the EICAR test file, and check your ClamAV installation’s log for a line like this to verify all’s working as before, but with your own up-to-date copy of ClamAV (which can be heavily customized now too):

instream(127.0.0.1@XXXXX): Win.Test.EICAR_HDB-1 FOUND