It's not in RFC2821 but sending a X-Priority might do the trick. Outlook Express seems to think a priority of 1 is urgent. 
   $smtp->data();
   $smtp->datasend("To: postmaster\n");
   $smtp->datasend("X-Priority: 1\n");
   $smtp->datasend("\n");
   $smtp->datasend("A simple test message\n");
   $smtp->dataend();

[download]
Based on the Net::Smtp docs.

gav^

In reply to Re: send mail using SMTP by gav^
in thread send mail using SMTP by Anonymous Monk

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