Archive for the 'E-Mail' Category

Publish and Update a PGP Key

I still keep a rather old PGP key around, and I have extended its lifetime by changing its expiry date. Something I would not recommend, because everyone with an old copy of the key in their keyring gets an “expired” warning or error.

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SMTP TLS Reporting, policy viewer

Screenshot of viewer webpage

For an easy way to lookup a domain’s SMTP TLS Reporting Policy try my nice MTA-STS Policy Viewer.

After writing the first notes on SMTP TLS Reporting I thought it would be nice to see all setting on one page, without using multiple tools and lookups for DNS and HTTPS data. The first iteration was a shell script, and the second iteration was a Python function. With some more fiddling I set it up as a Google Cloud Function, with a simple web frontend.

SMTP TLS Reporting, first data

The SMTP standard is just as ubiquitous as it is ossified and hard to change. Thus all newer RFCs follow similar patterns of a) adding optional extensions and b) providing feedback loops to detect usage, problems, and abuse of these extensions.

One more recent extension tries to enforce TLS transport between mailservers. This sounds very simple (and would be very simple if one could change the SMTP standard to require TLS), but is not trivial when compatibility is necessary and all TLS policies are “opt-in”.

SMTP TLS Report Chart
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I recently updated my small mailserver and finally configured DKIM. But another change was easier and still had more impact: installing postwhite. This little tool takes a list of mail domains, then uses their SPF records to derive a list of their outgoing mail servers, then writes this list into a postscreen whitelist configuration. The current default setting contains 43 domains and generates a whitelist with nearly 2000 lines (each containing an IP or subnet). Everything is nicely scripted and can run as a nightly cronjob.

This setup eliminates my biggest problem with greylisting, which is Office356. Their combination of long email resubmit intervals and using multiple cluster servers for delivery attemps always lead to long delays before I received email from Microsoft or any company using Office356. (BTW, I really like greylisting but this is its biggest design problem: it works for single SMTP servers and enforces certain behaviour, but does not and can not consider clusters.)

My First FreeBSD Port

A nice surprise last week: textproc/libcrm114 became my first official FreeBSD port.  :-)

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I released my first CPAN module.

I finally played with libcrm114, a C library that implements several text classification algorithms. It is a potential replacement for the mailreaver.crm tool, which is the basis for my SpamAssassin plugin. Read the rest of this entry »

my mailserver grows up

Yay, I received my 200th spam mail after I set up my own mailserver in January. – Now my SpamAssassin can use its Bayes classifier.  %-)

Procrastination @ work

erfassen wir doch mal die SpamAssassin-Scores…
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