Postgrey (Re: impersonating Juan, a quick test)

[Greg Newby]

On Sun, Jul 14, 2019 at 07:43:19PM -0300, Punk wrote:
> 
> 
> 	sorry for the duplicated posts. So while on the topic of email systems, there's been some change somewhere  - either cock.li... or the list's server I'd guess - and since a month or so I have to send the same message multiple times (around 4 usually) until it actually gets posted. 

In case this helps: Just yesterday I sent a longish message about the server setup for the system that is hosting this cypherpunks@ list.

One of the components is postgrey (which I misspelled postgray). When a message arrives from an unknown host, Postfix rejects it with a message to try again later. This is extremely effective against hit-and-run spam and similar annoyances.

I've found that there are lots of organizations that do not follow the RFCs for email properly, and do not try again. Lots of banks and ecommerce sites seem to write their own mail transport agent (MTA), and do not try again after getting the postgrey message.

It seems possible this is what's happening to your messages. If your service is using an MTA that doesn't try again - or if it tries again, but from a different IP address - the message might not get through. You should get a bounce saying it couldn't be delivered (anywhere from 30 minutes to 7 days later), but organizations that write their own MTAs might not handle error delivery that well, either.

If you have a message that doesn't seem to get posted, please forward me the message and I'll mine the logs to see what happened. There are plenty of other possibilities that might cause this, but postgrey is one that we can investigate easily enough.

Best,
 Greg