Clamd keeps crashing

Directadmin has been running flawlessly for months on a vps with 2GB ram. I use clamav for scanning email.

Since a few days clamd uses all available memory of the VPS, about 512MB, and then crashes. Again and again in a 1-minute loop:
clamd crashes -> clamd starts again automatically -> clamd reaches 512MB memory usage and crashes again.

Already tried a reinstall of clamav and some tweaks in /etc/clamd.conf (less instances, less connections, smaller queue...), but for now the problem persists.

Does anyone have any suggestions for lowering the memory usage of clamd?