"can't convert download 917 avast. com (unknown 80)"

When I went into e-mail this morning Avast gave the error message:
“can’t convert download 917 avast. com (unknown 80)”

What does this mean?
Will I get further updates?
How can I resolve this error and complete the update?

I don’t think it is related to having gone into e-mail, but a failed auto update.

The error you reported is often associated with firewall blocking of the update, ensure your firewall allows avast.update. If it does delete the entry for it and do a manual update and reconnect to the internet, this will force the firewall to ask permission again.