How many emails can I send via SMTP? Is there a limit?
Outbound email messages are limited to 500 per day. Each message can be sent to at most 100 recipients, and each recipient of a message counts as one email toward the 500 email limit. For example, if a message is sent to 50 recipients, this message counts as 50 emails.
In an effort to help protect all of our customers from spam, Yahoo has become more aggressive in its requirements regarding SMTP limits. In addition to placing limits on the number of emails you can send from your desktop email software each day, we may reject connections that don't conform to Internet best practices.