Received: from D6GKFL21 (AC8B72F2.ipt.aol.com [18.104.22.168])
by smtp-dtc14.proxy.aol.com (8.12.11/8.12.11) with ESMTP id j4PFebsO027589;
And a few more aol.com lines, before it gets to my local servers whose names I recognize. Even when I use that computer and Outlook to send using an SMTP server which isn't Netscape's and isn't the same as the To address. AOL shouldn't have anything to do with that at all.
So either Outlook is lying to us and using an AOL SMTP server for some reason, or netscape.com is somehow redirecting all SMTP traffic (by port, maybe) to an AOL address.
Will attempt to diagnose which of these this is by using Thunderbird. But in the meantime, has any of you ever heard of something like this? It seems bizarre to me. And I never would've guessed that AOL is the cause of this problem...
Edit: I'm now 95% sure that it was my ISP's fault. Despite their protestations, Netscape somehow redirected all SMTP traffic to themselves (or maybe I never tried to send it anywhere else, and Outlook somehow cached the SMTP address) and limited the number of recipients per outgoing email. Switched ISPs and it seems to work. Still need to test some things, though. (Like why the new ISP broke internet connection sharing.)