Measure 3 - Beg recipient's IT department to delete email
If you know an email has been sent and you definitely don't want the other person to read it, another way you can try to remove it from existence is by calling the IT department of the organisation you've sent it to and plead for them to delete it. It's very unlikely this will work if your email has been sent to an email address ending in gmail.com, yahoo.com, outlook.com or other major webmail providers, as they have policies against allowing this. But if you've emailed an Australian company that manages its own email, for example, then it's worth a shot. Depending on their IT policy - and how they feel about the situation - it might just work. But you'll need to be quick, as the recipient may have already downloaded it from their workplace's mail server.
Measure 4 - Recall the message
Some versions of Outlook allow you to recall messages sent to other email users who use Outlook. The success or failure of a message being recalled depends largely on a recipient's settings in Outlook and also whether they actually want to let you recall it - a reason why this method is probably not the best to use. There's also the fact that recalling a message will generally inform the recipient that the email exists and highlight the fact that you want to recall it.
Measure 5 - Admit defeat and apologise
If all of the aforementioned methods do not work - or you just don't want to try them for whatever reason - then an apology might be in the works. The sooner you apologise the better.
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