I have a website that takes paid subscriptions. 10 days before a
subscription expires, a script that runs via cron sends out an email
notification.

So I have sitting in my in box an email from an automated spam blocking
program asking me to verify that my email address is real before it will
send an email with my from address to the recipient.

My email address is real, but the email in question may not be. I send
out a dozen or so automated emails every night, but my email address is
also forged onto hundreds of spam emails every day. The spam blocker
does not give a subject line for the email in question or any of the
content, so I can't tell whether it came from my site, or it is spam.

The recipient's email address is not in the list of emails that were
sent out last night, but there are other ways a legitimate email could
be sent from my site. I am inclined to ignore the email from the spam
blocker. If the email in question is spam, I don't want the recipient to
be flooded with spam emails with my return address forged onto them.

So why can't spam blockers include the subject line of an email that
they are questioning? Don't they know that not all generated emails are
spam?