Some people have had difficulty posting from various mac addresses (mac.com, icloud.com and me.com) since Yahoo will have one address on file (e.g., mac.com) but not see the one you are posting from as the “same.” Frankly, to yahoo mac.com and icloud.com extensions are apples and oranges to their system.
Here's how to add the other emails (me.com, mac.com, icloud.com) to your preferences. If this doesn’t work there are other things we can do to help, but try this first and see if it fixes things!
