This morning Exim complained about ClamAV daemon not being present. Upon inspection it turns out that ClamAV was complaining that its databases were broken. This may be linked to all the restarts we made yesterday to test various combinations of programmes and see what made X crash. Anyway, removing the databases in
/var/lib/clamav/ then running
freshclam (which takes a while, as the entire database has to be re-loaded) fixed the problem.
It’s unclear whether e-mail gets bounced or simply delivered without scanning when the malware ACL fails.