[Mailman-Users] Messages delivered out of order and delayed

[Carl Zwanzig]

On 9/13/2019 6:59 AM, Veronica Morris wrote:
> For the past few months, we've noticed that messages are arriving out of
> order, and sometimes are delayed by hours or even a day!

Please remember that email is not a "real time" communication system; might 
look like it sometimes, but it's always "store and forward".

> The kicker is that the delivery issues are not the same for everyone.  Some
> people will get a particular message immediately, while others will get
> that message in an hour, and others in a day.

For email, this is not abnormal. Mailman will generally "send" all of the 
messages at once, but once they're handed off to the server, they're out of 
mailman's control. That server and succeeding ones can have any number of 
delays occur (name resolution, receiving server is busy, held for spam 
checks, etc). Also, once the sending server gets the email to any large 
provider (i.e.gmail or yahoo), -they- may not process that immediately.

In short, there isn't much you can do about this. If mailman is 
personalizing messages, that can cause them to be sent individually instead 
of being batched, but in most cases you need that personalization anyway for 
things like DMARC mitigation.

Later,

z!