Inject log entry every 15 seconds

I get this in the `/var/log/mail` every 15 seconds:
```
mx roundcube: <9cks31r1> template_inject : inject: core-pref/[plugin.responses] text thank you (key=d228c9362570e8e0)
```
and 2 other entries.
I have disabled the plug for now. What could be causing this?