No. Just can’t use apple to send yahoo email
Now. A new problem. This seems to be since apples last software upgrade.
I’ve got Yahoo mail and I have no problems at all. I did the upgrade within hours of it coming out.
I would suggest first deleting your Yahoo account “on the Apple device” - then setting it back up again.
If that doesn’t work, then I would do a full and total backup on iTunes, then when you’re assured the backup is there and is safe — then RESET your device to original factory condition, and restart the device and use your backup to bring it back to your previous state.
If that doesn’t work, then I would head on down to the Genius Bar at the Apple Store and have them look into your device.