Alright ya'll. I may have found another issue, but maybe it's just me.
Arising from the loop idea that was brought up as a temporary workaround-
if curl_slist_free_all is called and I loop around and add a recipient
to the same slist I just free all'ed, it creates an infinitely linked
list- so you need to append to a NULL slist (see attached example).

Could someone tell me why the value from curl_easy_perform() on an
invalid address returns CURLE_LOGIN_DENIED and verify that it is unique
from invalid login information? It seems to me that this is probably not
an accurate error code, since to my limited understanding of mail
servers, it is possible to be required to Login to a mail server to send
mail. (though this would also prevent the recipient from receiving the
email in question- it would just be more difficult to trace the real
problem with sending that email)

By the way- thanks for your attention to the last issue. I appreciate it.

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