Email systems such as Gmail like group email messages into "conversations", such that messages A is presumed to be a reply to message B. There's lots of methods they use to determine what message you're replying to, such as the Subject: header or the In-Reply-To: header.
However, since automated emails tend to sometimes reuse subject lines (e.g. "Monitoring failure on server"), often the mail service will assume that a given email is actually a reply to a previous message with the same subject line, even though the two are unrelated. This can lead to confusion and clients potentially missing an important notification.
How Can overcome this issue?