bug: if email fails to send for any reason, newly found domains will be lost

[kristovatlas]

If an alert email fails to send, the newly found domains will be marked as "found" and won't be considered for an alert during the next invocation.

Some possible solutions: -track not only whether domains were previously found, but also their alert delivery status -(easy) just log the domains found if the email alert fails.

Note that the email can fail to be delivered even if not rejected by the SMTP server (e.g. filtered as spam later in the delivery process) but there's not much we can do about that.