[Gloucs] Spam to unique email address

[Paul Broadhead]

Slightly off topic for Linux but I know we have some experts
around....

Whenever I subscribe to an on-line service I use a unique
email address prefix before my normal @domain, like the one I use
here.  Now if this email is exposed on the internet, I get spam, lots
of spam. For example, if used on a public mailing list. However, when
the service does not publish my email address, I expect only proper
service email and no spam.  This is almost always the case. Very
occasionally, I do get spam sent to such email addresses.  One such
case happened last week so I contacted the service support and asked if
they could explain.  I have had a very reasonable exchange with the
these support folks who appear to be taking the situation very
seriously.  They assure me they have not lost or given my address to
anyone else and that their servers are not compromised. Assuming
things are OK my end too, the question is.  How can this be explained?

One explanation is that spammers are just guessing valid email
addresses. Any thoughts?
regards,
Paul