Since you are running this through COM, you still have to log into the server at some point with a user ID. It is likely that Lotus Notes is just sending it this from your email account because you have logged in with it to run you COM application. Whether through COM or straight LotusScript, the Lotus Notes uses the mail properties of who ever is running the code or last signed the agent. Simply choosing to create the document inside of a specific mail database does not mean that the message won’t appear to come from the ID that created the message.
You can try setting the From, Principal and the Replyto field to the email account associated with the mail database, but that does not always work, at least in my experience. Sometimes this is enough, but several SPAM filters today check to see if the person sending the email is the same as the From address and if not, treat it like SPAM.
Another option might be to login to Lotus Notes with an ID and password associated with that mail database via COM. Then when you send an email message Lotus Notes will apply the correct account name. This would mean that each of you users of the Excel file would need a copy of the ID installed on their machine so that they could log into Lotus Notes when prompted by COM with the correct ID.
A third option would be to create the account associated with the mail database and add a scheduled agent that sends out emails based on some criteria you set. Then, via COM, your users can still use Excel to ‘upload’ the message to the mail database. Your schedule agent would check every X minutes to for a new message and then mail it out using the email account associated with the database.
Hope this helps, or at least someone else comes up with a more concrete suggestion.