how can I tell if my email to another recipient has been marked as "Spam" ?

Answer 1

You can't, and won't - for a very good reason:

If such information were available, then 'spammers' would use that knowledge to circumvent any detection mechanism that is running on the recipient's end and cause more mischief. Therefore, if any of your messages are being treated as spam, quite often, you won't hear about it.

The best way to verify this, is by asking for a conformation - or 'request read receipt' when composing an e-mail. Also, it would help to avoid using certain words and emphatic gestures that normally trigger spam detection software (such as viagra, stock on the rise!!! etc.)

Answer 2

Yes you can find out if you're on a list I had an email come back yesterday. Spammers can make offers all day long but I couldn't write myself a reminder email ,but if I wanted a bigger penis I got 5 offers on that yesterday.

They do have a long and drawn process to see if you're on a spammers list

failed after I sent the message.
Remote host said: 550-Message contains blacklisted domain (nuxit.net)
in [ws]. See
550 http://www.surbl.org/lists.html

You might also do some searches on "SPAM COP"