Sheldon had deleted the first two emails in the conversation because the subject line contained the word "Cleaning". But he read the second one, because it was from Brian, and Brian often made other people uncomfortable with his bluntness, which was a quality Sheldon respected. He had always thought the world needed more bluntness. Granted, this was much more enjoyable when it happened in meetings or otherwise in-person and the shock on other persons' faces could be observed.