Saturday, December 28, 2019

Some mailman list members don’t receive any mail

I continued with #3339.

One possible explanation is that we have no DMARC record. According to

On I found valuable information:

A DMARC record is defined in the DNS file for our domain, i.e. at It allows us to indicate to a mail receiver (e.g.

  • the mechanisms used to authenticate its email (DKIM, SPF or both).

  • how to handle mail that fails validity checks.

  • Optionally request the receiver to send a feedback report, allowing the sender to analyze what’s happening

IOW before writing a DMARC record I must setup SPF or DKIM. DKIM is more complex than SPF, so I choose SPF.

The SPF information must be defined using a standard TXT resource record (RR) that looks like this:

name ttl  class TXT  "v=spf1 ..."

But what to put into that "v=spf1 ..."?

Notes from How to Build Your SPF Record in 5 Simple Steps:

To protect your customers, your brand, and your business from phishing and spoofing attacks, you must authenticate your email. An SPF-protected domain is less attractive to fraudsters and is therefore less likely to be blacklisted by spam filters.

Step 1 : identify which mail servers you use to send email from your domain.

It is important to create SPF records for all the domains you control, even the ones you’re not mailing from. Why? Because once you have protected your sending domains with SPF, the first thing a criminal will do is try to spoof your non-sending domains.

If I understand this page well, our SPF record is simply:

name ttl  class TXT  "v=spf1 ip4: -all"

Actually this means that I add “v=spf1 ip4: -all” in the DNS file setup form at the right place.

Now for the DMARC1 record, this is another TXT record with the following options:

v=DMARC1; p=quarantine

Where v=DMARC1 is mandatory and p must be either none or quantine or reject. For documentation about the allowed tags in a DMARC record see

The actual zone file looks as follows:

; 2 TXT record(s)           IN      TXT     "v=spf1 ip4: -all"           IN      TXT     "v=DMARC1; p=quarantine"

When I first tried it still said “No DMARC Record found”. That’s because it takes some time for the DNS record to get replicated.

At a first attempt I said “v=DMARC1 p=none” instead of “v=DMARC1; p=none” and mxtoolbox correctly reported a Syntax Error.

Oops, and I must probably say “v=spf1 ip4: ip4: -all” instead of “v=spf1 ip4: -all” because LF uses the ovh relay server, so receives my mail via this.

Note that above examples are not yet the solution. The journey continues Sunday, December 29, 2019.