I've been searching for an explanation on this matter, but the closest I've come to finding related discussion is users concerned with sending from secondary SMTP. Where my concern lies is in the "To" field. Here's some info to help the discussion:
domain1 email is only accessible via VPN OWA. Domain2 email is accessible via Outlook and OWA, but primarily through Outlook.
User has two email addresses: first.last @ domain1.com (f.l @ d1.com) and first.last @ domain2.com (f.l @ d2.com). In Outlook Properties (domain2), I can see that this user has both email addresses as SMTP. If I try to send this user an email to f.l @ d1.com, the user will never see this message in the f.l @d1.com mailbox; however, user will receive the message in her f.l @d2.com mailbox. Mind you that f.l @d1.com is in fact in the "To" box, and nothing is in either "Cc" or "Bcc" boxes, so there's no apparent explanation as to why the diversion happens.
Curiously, though, if I login to the domain1 VPN, and then send a message to user's f.l @d1.com email address, the message will be sent to the correct inbox, her f.l @d1.com account mailbox.
Upon looking at the Outlook Properties of my display name in Outlook, I see that I only have my f.l @d2.com address next to SMTP (which is normal, as opposed to the user's Outlook I'm inquiring about)
So, I can obviously determine that Outlook is silently diverting the mail going to f.l @d1.com to the f.l @d2.com mailbox, but why? More importantly, what can I tell the system admins to get this fixed?
Please don't mind the spaces in the email addresses, I had to do this in order to get my question posted.