If you send email to 5,000 people using standard PHP tools, your ISPs might be blocked in seconds.
I think you already read below articles…
Amazon Simple Notification Service Command Lines
Emails are not working on server?
Email’s Major Sections
Header – From, To, Subject, Date, Message-Id
Body – HTML / Text
Server must have …
* Dedicated public static IP address
* Reverse DNS record for IP address
* Contact info in WHOIS record
* Mailbox Tracker
* SPF Records
* Signed message using DKIM
* VERP – Variable envelope return path
* Automatic Bounce Handling
* Email Scheduler
* Email Subscribe / Unsubscribe
* Keep the IPs white-listed
Limit on servers
500/per hour on the Shared servers is the limit.
Other References
http://framework.zend.com/manual/en/zend.mail.html
http://pear.php.net/package/Mail_Queue
http://www.phplist.com/details
http://wiki.e107.org/index.php?title=Bulk_mailer_interface
http://swiftmailer.org/
http://sourceforge.net/projects/phpmailer/
http://mlmmj.org/
http://www.gnu.org/software/mailman/index.html
