Manual:$wgUserEmailUseReplyTo/ja

詳細
に が設定されている場合、利用者間のメール内で、送信者である利用者のメールアドレスを　From 行に直接記載するのではなく、Reply-To ヘッダーのみに記載します. メールは  から送信されたように見えますが、返信は利用者が利用者間メールを送信する際に使用するメールアドレスに届きます.

送信者である利用者のメールアドレスを From: 行に記載した方が、見た目がよく便利かもしれません. But there are several reasons why setting of 'false' may not be desired. They are:

This behavior can cause email messages to be penalized for SPF violations (since the wiki server isn't authorized to send messages on behalf of other domains) e.g. anyuser@userdomain.com is not authorized to send mail on yourwiki.com domain.
 * Putting the sending user's email address in the From: line doesn't as clearly differentiate user-to-user email (an email sent via the wiki) from directly sent messages (emails sent from an email client).
 * Another concern is that some mailers (like sSMTP) will use the From: address as the SMTP envelope sender (the generator of the email message).
 * MediaWiki installations on a shared server may fail to send user-to-user email due to spam prevention by disabling open mail relaying.