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It would take a bit longer because you're uploading your email to your mail server.  It will then be put into queue along with other people's email.  When it time for your mail turn, it will then be sent to the destination's mail server.  But first it need to find out where the destination mail server is.  It has to hit the DNS server of the recipient domain.  Once found, then it will send it to that mail server. 
 Then the recipient mail client will have to check the server for new mail every certain interval.  Once it sees a new email, then it'll be downloading it for viewing.
As long as the mail and DNS server are working, it will be done in less than 5min.  Still faster than snail mail.