[AusNOG] [DKIM Failure] Re: Anyone knowledgeable from Mimecast here who can contact me off list?
Two Fat Monkeys - Dirk Bermingham
dirk at twofatmonkeys.com
Tue Oct 19 13:23:32 EST 2021
Whilst we’re living on the edge here….
To quote the RFC:
”SPF implementations MUST limit the number of mechanisms and modifiers
that do DNS lookups to at most 10 per SPF check, including any
lookups caused by the use of the "include" mechanism or the
"redirect" modifier. If this number is exceeded during a check, a
PermError MUST be returned. The "include", "a", "mx", "ptr", and
"exists" mechanisms as well as the "redirect" modifier do count
against this limit. The "all", "ip4", and "ip6" mechanisms do not
require DNS lookups and therefore do not count against this limit.
The "exp" modifier does not count against this limit because the DNS
lookup to fetch the explanation string occurs after the SPF record
has been evaluated.”
Chris’ SPF was even more borked earlier… Those includes need to be trimmed a bit further to comply…
From: AusNOG <ausnog-bounces at lists.ausnog.net> On Behalf Of Noel Butler
Sent: Tuesday, 19 October 2021 1:11 PM
To: ausnog at lists.ausnog.net
Subject: [DKIM Failure] Re: [AusNOG] Anyone knowledgeable from Mimecast here who can contact me off list?
This is likely off topic for this list, but anyway, since I live on the edge...
By my count there is only 3 not 10 mechanism lookups (and show me an implementation that actually stops at 10), I'm not so sure they should be counting the includes includes/a/aaaa's either, only the include itself, as includes are typically out of your control (it has been a very long time since I read that RFC so may be wrong)
Anyway, if that was the issue, it would have surfaced long before now surely.
If I was a betting man, I'd say DNS caching is the cause, if I was a betting man, I'd also be betting someone didnt drop a TTL when preparing for the change, so will have to wait till records refresh.
Of course all this is assumption because OP never posted the actual error message.
On 19/10/2021 09:07, Andrew Oakeley wrote:
If I was you; I would start by fixing your SPF.
This will show you the errors
From: AusNOG <ausnog-bounces at lists.ausnog.net> On Behalf Of Christopher Scholfield
Sent: Tuesday, 19 October 2021 7:04 AM
To: 'AusNOG Mailing List' <ausnog at ausnog.net>
Subject: [AusNOG] Anyone knowledgeable from Mimecast here who can contact me off list?
Yesterday we changed mail filters, Mimecast is the only email provider that has been rejecting our emails due to SPF problems for the last 20 odd hours. Mimecast technical support has told me their customers who aren't getting our emails need to contact them so their tech support can explain how to bypass their mail filters for our mail server.
I'd rather work with someone at Mimecast to resolve the cause of the problem.
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