It is necessary to create a permanent transient failure
Update: 4.xx vs a 5.xx was the least of my worries when I found that not all mail servers were returning errors according to the standard. I prefer to treat all types of bounced mail as failures, but I leave this question here in case it gets a response and helps someone else.
I was tasked with writing a program to read a POP3 account and distinguish between mail returned as a permanent failure (delivery status 5xx) and a permanent transient failure (delivery status 4.xx), retrying 4.xx DSNs, and flagging the message as bad for DSN 5.xx. It's easy enough to manually edit the DSN body to change 5.xx to 4.xx, but management would rather return the "real" 4.xx I'm in a lot of trouble.
The test environment is Windows 2003 Server with MS SMTP and POP3. I have already tried exceeding the quota on the target email (5.xx) and blocked the account (2.xx and they cannot receive email).
This is for lease termination notifications, in case anyone is interested, so we are interested in flagging emails as bad or retrying, the denial was not permanent.
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Creating a transient failure is not that difficult. Some come to mind:
- Some local alias extension error (it could be more of a Unix thing)
- DNS lookup timeout (change your nameserver to something silly, or set up a subdomain pointing to a non-existent nameserver)
- Start mail server from disk space
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