sendmailのログを見てmxの優先度が無視されてないかと思った場合

MXレコードには優先度というものがありますね、こんなん

example.com 3600 IN MX 5 mail1.example.com
example.com 3600 IN MX 5 mail2.example.com
example.com 3600 IN MX 10 mail3.example.com
example.com 3600 IN MX 10 mail4.example.com

ブラックリストとかやらかして、全てのメールサーバーにBANとかされていると、メールログには

relay=mail3.example.com
relay=mail4.example.com

しか出てこなくなります。

これは別に優先度の低いやつにしかアクセスしていないのではなく、最後にアクセスしたやつのログが残っているだけのようです。

バウンスメールを確認すると、

... while talking to mail1.example.com.:
<<< 554-mail1.example.com
<<< 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact
 the intended recipient via alternate means.
... while talking to mail2.example.com.:
<<< 554-mail2.example.com
<<< 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact
 the intended recipient via alternate means.
... while talking to mail3.example.com.:
<<< 554-mail3.example.com
<<< 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact
 the intended recipient via alternate means.
... while talking to mail4.example.com.:
<<< 554-mail4.example.com
<<< 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact
 the intended recipient via alternate means.

こんなんでていると思います。