optimisation sending mails

hi, I need every week to check mails in a database and send them on e-mail to a mailinglist server to synchronise the datas. I work with two mailing servers and 4 mailinglists (2 on each server). so I need to send 4 lists in mail : one to server 1 with liste A one to server 1 with liste B one to server 2 with liste C one to server 3 with liste D I would like to know what is the best way for optimazing the server resources : To send mail during browsing of the record set of the database every time I change liste or browsing all the recordset pushing the datas in a array every time I change mailinglist and when browsing is closed send browse the array and send the four mail with the mail() function ? Is there a solution which permits sending all my mails (4) in one smtp connextion ?