Interesting that you use Rogers. I have about 60 clients who use it as well as myself. I am quite familiar with Rogers.
First understand that Rogers uses Yahoo Yahoo has been either in or out of bankruptcy or close to it repeatedly. It's owner Verizon has written off their acquisition. I do not think Yahoo has much of a future. Anything that involves Yahoo has to be viewed with a lot of concern. I have therefore recommended to my clients they do NOT use Rogers email addresses as their primary. Google is another story. May 30, 2022, Google will effectively end WLM users ability to use Gmail through WLM. So Gmail is not a good alternative. I believe Microsoft's Outlook may be an alternative, but I do not want to predict how long that will be the case. There are a lot of providers. Some very good. You can also pay for an email service. The fees are not big, but can provide vastly superior service.
You need to understand that none of these free mail services want you to use WLM (or any other mail app) because they depend on showing you ads in their webmail systems and WLM bypasses that. Gmail claims it is for security purposes, but that is just what they say.
Rogers cannot directly do much with Yahoo. Rogers techs sort of do their best but ONLY if they actually send a report to Yahoo are you getting any kind of useful answer. Even then, given the questionable situation at Yahoo, its a tough guess.
I have a Rogers address too. I just now tried to send a BCC to myself and it fails. So the problem you are seeing is confirmed. If Rogers blames it on WLM, they are full of it. They just do not want to deal with WLM, and by policy want you to use webmail.
In short, the BCC problem you just described tells me that your email service at Yahoo is corrupted. The problem has nothing to do with your computer or even Rogers itself
Bottom line, like me and my clients, find another useful and quality mail provider.