@より前がランダムっぽい文字列のアドレスへは、plalaではメールを送れないのでしょうか。
以下のエラーが返ってきて、送信が正常に完了しません（foobarの部分が実際はランダムっぽい文字列）。

This Message was undeliverable due to the following reason:

Each of the following recipients was rejected by a remote mail server.
The reasons given by the server are included to help you determine why
each recipient was rejected.

　　Recipient: <[email protected]>
　　Reason:    Invalid recipient: <[email protected]>

Please reply to [email protected]
if you feel this message to be in error.