(Yahoo/OutlooK : E-mai) 想知收件人是否已開啟?

個人所知
yahoo mail冇得查收件人是否開啓，只有，你打錯收件人個mail，佢就會話給你知

Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following
addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
但，不會查對方有冇開過

outlook就可以
去工具，選，
要求讀取回條(T)

咁就得