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Depending upon the reason an email is bounced back, most smtp servers are configured to retry a certain number of times - like every 12 hours for 4 days. Varies by smtp server configuration.
Check with your ISP and see if your account has a postmaster box for dumped emails. Then what you do depends upon how programmable your ISP allows your smtp server to be.
A semi-manual alternative is to use a specifc acount to send them, and set up Outlook or some other client to read-only that account and handle anything that's returned to the account manually.
Email can bounce for a variety of reasons but a good rule of thumb is to delete the account from your mailing list after not being able to deliver for two or three successive mailings. Upon a successful delivery, you'd set the counter back to zero,
Some of the scripting sites have sample code for this, but it really depends upon how much access to the mail queues your ISP allows.
Your basic process is..
- Determine if accessing the smtp queues or catching email via a client will work best for you.
- Determine which emails are undeliverable as of the final server attempt to deliver them. Requires filtering/tracking to id the final attempt. In the example above, seven bounces would indicate it got through on the eighth attempt. Eight bounces would indicate it never got through.
- Either change the maillist db or create a new db to include the user id, count of unsuccessful attempts, and date of last unsuccessful mailing. You may also want to check the email headers for the reason and only count certain non-delivery reasons.
- About a week after a mailing, reconcile the final bounces with the data base.
- If the email id has no bounce count in the db, add them
- If the email id has reached their consecutive bounce limit, zap them from this and the mailing list db.
- If the email has a bounce count, but is not in this latest batch of undeliverables, zap the bounce count.
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