You'll see this in the next 16 minor. We will only show messageid in the SMTP logs if it's provided by the sending server. We always show the messageID for a local delivery in the delivery logs.
Example from SMTP
[2017.12.19] 14:40:19 [10.1.1.185][6642073] Data transfer succeeded, writing mail to 513980188002.eml (MessageID: <messageid>)
Example from Delivery
[2017.12.19] 14:40:26 [88002] End delivery to testguy@st14.com (MessageID: <messageid>)
Matt Petty
Senior Software Developer
SmarterTools Inc.
www.smartertools.com