Yahoo Mail Settings

Thank you for writing to Yahoo! Mail.

To facilitate the smooth flow of messages between legitimate senders and
Yahoo! Mail, we offer the following recommendations:

Limit the messages you send per connection

Yahoo! Mail accepts a maximum of 20 messages per SMTP connection. We
encourage you to cap the number of messages you send to Yahoo! Mail to
fall within this per-connection limit.

When this limit is reached, no further messages will be accepted for
delivery as our server automatically terminates the connection (without
giving an error code). If you are sending messages to a significant
number of Yahoo! Mail users, the suggestions below will help ensure
uninterrupted delivery for your messages.

Re-establish connections if you do not get an error code

When our server terminates your connection after 20 messages have been
accepted, you may try to reconnect to our MX servers immediately
thereafter.

Open concurrent connections

You may open concurrent connections from the same server to facilitate
efficient transmission of your messages. However, while we do not
publish specific guidelines for the numbers of connections you can
concurrently use, we ask that you treat our resources with respect. The
more you take, the fewer there are for others, which may force us to
de-prioritize connections from your server(s).

Thank you again for contacting Yahoo! Mail. Your case number for this
issue is XXXXXX. Please reference it in all future communication about
this particular issue.

Regards, Hank
Yahoo! Customer Care