To which domains are you sending? Gmail / Yahoo Mail or some other?
We know that Gmail are choosing to dump mail into Spam folders without checking the contents for spam. If you know your mails aren't arriving then presumably you have contact with the recipients so do please ask them to look in their Spam folders for your mail messages, select and mark as Not spam to return the messages to the Inbox and that will also tell Gmail not to dump your future messages into Spam.
