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Postwhite FAQ

Q:What features are planned in the future?
A:Quite a few, actually. However, implementation depends on the public response to Postwhite and whether people or institutions are willing to sponsor some of the development work. This list is not concluding and not really priorized:
  • Currently, domains have to match 100%. In real life it would be better to default to the second level domain to match, so a sender from www.domain.tld would be allowed if domain.tld was on the whitelist.
  • Add SPF to make sender forgery a big deal harder.
  • MTAs with many users might prefer the use of email recipients which would be protected by Postwhite based on recipient email convention rather than listing in recipients.yml to offer whitelisting with minimal configuration effort. In other words: arthur@dent.tld is not protected while arthur-safe@dent.tld (like all -safe email addresses) is protected.
  • Currently, non-whitelisted emails result in REJECT while whitelisted emails result in DUNNO. This could be made configurable to support other results such as DISCARD.
  • People who prefer to use mailing lists with web frontends might like a hide command which whitelists a sender, yet incoming emails would not be delivered but silently DISCARDed.
  • Currently the whitelist checks against the sender email. This works for mailing lists if you subscribe to the digest, but not if you subscribe to direct mails. A solution for this could be the extension of the whitelisting in order to check against other request data such as the client_name (aka: sender MTA host).
  • Postwhite is not testen in high traffic environments. If it misbehaves in such a setup, a migration of the internally used GServer to EventMachine could be a solution.
Q:Does Postwhite interfere with the greylist service?
A:No - if you configure things correctly. It's important you add Postwhite before the greylist service in smtpd_recipient_restrictions. Postwhite replies REJECT if a sender is not on the whitelist and DUNNO if it is. This means that all restrictions after Postwhite will be evaluated as well. However, there's an exception to this: If Postwhite is in learning mode, the reply is OK thus skipping subsequent restrictions. This is necessary as the greylist might initially block the incoming mail and thus cause troubles and duplicates.

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