Comment 5 for bug 261249

They did change the on disk signature database format once, but the old versions could still get data across the network. The impact of that was that libclamav3 and libclamav4 could not reasonably be made co-installable.

It's mostly ABI/API changes in libclamav and changes in options/names for clamscan. This isn't generallly problematic for clamav itself, but for the libclamav and clamav rdpends, but those will all stay in Universe, so I don't think it directly relates to the MIR. Clamd integration (which is what is used for the use case that's planned to be supported with amavisd-new) is stable (unchanged since at least Dapper AFAICT).

Fortunately Debian actively maintains this package and with the new pkg-clamav team should do even better, so we can largely benifit from their work.

I think the biggest supportability issue for this package is the volume of security updates. Since clamav always (well almost always) commits their security updates right before release it's generally reasonably easy to work out what needs to be dealt with.