How can I tell if someone is reading email I sent to them through another provider other than Yahoo?

I have been trying to get in touch with this person. I have an email address for him but I don't know if it is still working. It is a military one. I don't get any failure notices back. Is there anyway of tell if he is receiving and reading the messages I send?
How can I tell if someone is reading email I sent to them through another provider other than Yahoo?
www.didtheyreadit.com





The first 10 emails you track are free. It has had some bugs at times, so it isn麓t entirely reliable, but well worth it when it works--especially if you麓re in it just for the 10 free emails.





--This service sends you an email when the reader opens the email, and another when they finish reading it, to let you know how long they read it for.
Reply:Nope, the address is getting them if your not getting a failure notice. Maybe he doesn't use it anymore...
Reply:yes you can set up a cell phone alert for your phone which will tell you if he received your mail. If his mail still exists, you would know because you would get a mail daemon notice if it had closed.