Sometimes email messages are routed directly to a Spam folder, for one reason or another. Certain phrases and words in the message trigger this — e.g. “click here to unsubscribe,” “free money,” “viagra,” “$$$,” etc. Once a message lands in the Bulk/Spam folder, it is automatically deleted after a few days. If the recipient never checks this folder, they’ll never see the message. (I check mine, just for this reason).
One easy way to resolve this is to have the recipient add your email address to his/her address book. When your address is on this “white list,” all messages will be delivered to the Inbox, regardless of how many spammy phrases you include in the message.
Not sure how to deal with affiliate managers not receiving messages from affiliates, though.