Problems with mail() function

Hello. I wrote a routine that queries a table (Mysql) to pull about 300 records and record their emails. I iterate over this recorset invoking the mail() function to send an email for each record in this recordset. The problem is that on my providers server, there is a big delay before the script end execution. When it takes too long I hit the "stop" button on the browser, but when I do this the users receive the same email twice. Why is this happening? -- ************************************ Ivan R. Quintero E.* (507)228-3477 Aptdo 1263 * (507)228-9105 Balboa, Ancon * 612-1103 Republic of Panama * ************************************