|
|
|
|
|
|
by david-given
4135 days ago
|
|
|
This has been done; it's possible to exploit the SMTP rules to force the client to do proof-of-work before the server accepts the email. What you do is reply to the client's first connection with a temporary failure; this forces the client to cache the message locally and resubmit. On the client's second connection, you accept the message. It's called greylisting, and it works really well as a cheap and easy spam prevention mechanism. I wrote an implementation and used it for years as a first-line-of-defence; it let me use a crappy little 32MB ARM box as an SMTP server. (<plug> http://spey.sf.net </plug>) |
|
|