When someone uses SCF to send me an email, Yahoo always dumps it in the Spam Folder. Part of the problem is that messages from any Bulletin Board or Forum have different sender and reply-to addresses. I suspect it also happens with most other email servers.
It's not possible to "white list" the messages, because those lists are based on the sender's address which, of course, is likely to be different with every message.
The answer is to create a FILTER.

All messages from SCF use the same subject line, "
Sent From Stamp Community Forum by xxxx"
As you can see in the screenshot, the trick is to tell your email program that any message with "Stamp Community Forum" in the subject line should go in your InBox (or any other folder of your choosing).
In Yahoo, click on Settings, then Filters. Most email programs have a FILTERS setting somewhere -- check your options.
Hope this helps someone.
KirkS
[Admin: I wasn't sure what forum was most appropriate for this post, so I put it here.]