I'm using SmarterMail Enterprise build 7719 and noticed that system messages (or, at least the Internal Spammer notification: Settings -> Security -> Internal Spammer; not sure about others) don't seem to use the Daylight Time version of the time zone during DST. This causes Thunderbird (Version 78.8.1) to display the time an hour late under the Date column in the message list, and at the top of the message when you open it. Not a huge issue but I thought it was worth mentioning.
Webmail and desktop Outlook 2019 (Version 2102, Build 13801.20294 Click-to-Run, 64-bit) show the correct time. Also, all other "regular" emails show the correct time in all clients, including the -0500 offset in the headers. The time was shown correctly on these system message emails in all clients during Standard Time, with the -0600 offset in the headers.
The server and my time zone is US Central Time, which is -0500 (CDT) right now instead of -0600 (CST) like in the following real example from my server from yesterday (with only usernames and domains changed). 17:14:14 is the correct time; only the time zone offset is wrong.
Received: ; Mon, 15 Mar 2021 17:14:14 -0600
Date: Mon, 15 Mar 2021 17:14:14 -0600
Content-Type: text/plain; charset=us-ascii
From: "System Administrator"
Subject: Auto spam notification
X-SmarterMail-TotalSpamWeight: 0 (Authenticated)
This is an automatic spam notification message generated by mail.example.com
The sender firstname.lastname@example.org has exceeded the abuse detection rule of 50 outbound messages in 10 minutes.