On Thu, Apr 16, 2020 at 06:14:46PM +0200, Martijn van Duren wrote:
> On 4/16/20 3:58 PM, Jacky wrote:
> > Hi,
> > 
> > I am using Opensmtp 6.6.4p1. I am going to use Opensmtp as outgoing SMTP 
> > server, and use POP before SMTP method for authentication.
> > 
> > Is it possible for us to write and use custom filter ? If yes, is there any 
> > information / resources available in the web ?
> > 
> > Jacky
> > 
> 

You can get the manual here:
https://raw.githubusercontent.com/OpenSMTPD/OpenSMTPD/portable/smtpd/smtpd-filters.7

I don't believe it is 100% but still a good starting point.

Edgar

> There are a couple of filters available, but I'm not aware of how
> cross-platform available they are.
> From the OpenBSD ports tree there's the following written in go:
> - https://github.com/poolpOrg/filter-rspamd
> - https://github.com/poolpOrg/filter-senderscore
> - spamassassin via https://www.umaxx.net
> The latter has a couple of other filters, but aren't in the ports
> tree, so probably have a little less testing.
> 
> I have written filter-dnsbl and filter-dkimsign in C:
> - http://imperialat.at/dev/libopensmtpd/ (dependency for both)
> - http://imperialat.at/dev/filter-dnsbl/
> - http://imperialat.at/dev/filter-dkimsign/
> 
> I've got libopensmtpd to compile on Linux, but after that my need to get
> them to work on Linux disappeared so the filters themselves never got 
> there. If you want to use them I'm willing to help you set them up in 
> your environment and commit the changes to my repo.
> 
> Other filters are relatively easy to write, but I don't think the
> protocol is properly documented. You can look at this thread[0] as a
> starting point, but there have been some minor changes since then, so
> make sure to check your input.
> 
> martijn@
> 
> [0] https://www.mail-archive.com/misc@opensmtpd.org/msg03727.html

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