dovecot - Oct 2021 - Doveadm fetch slow and 100%CPU with a specific message-id

On Mon, 25 Oct 2021, Ron Garret wrote:
> Note that message-ids are not guaranteed to be unique.  During my test
> I found groups of as many as 20 different messages with the same
> message ID.  (Turns out this makes quite a reliable spam signal!)
It's by far not a rare situation: duplicate message-ids happen whenever
the sender names more than one local recipient during SMTP.  It's a wholly
unreliable way to indicates spaminess.  However, if a high proportion
of those recipients do not exist, ...

Joseph Tam <jtam.home at gmail.com>

On Oct 25, 2021, at 2:23 PM, Joseph Tam <jtam.home at gmail.com> wrote:
> On Mon, 25 Oct 2021, Ron Garret wrote:
> 
>> Note that message-ids are not guaranteed to be unique.  During my test
>> I found groups of as many as 20 different messages with the same
>> message ID.  (Turns out this makes quite a reliable spam signal!)
> 
> It's by far not a rare situation: duplicate message-ids happen whenever
> the sender names more than one local recipient during SMTP.  It's a
wholly
> unreliable way to indicates spaminess.  However, if a high proportion
> of those recipients do not exist, ...
I think you may have misunderstood.  What you say isn?t wrong, but in the case
of multiple local SMTP recipients, all of the duplicate messages will have the
same content.  What I have found is the same message ID in messages with (very)
*different* content (and often sent to the same user).  All of that has been
spam (and it is hard to imagine any situation in which it would not be).

rg