Elastic Email uses MessageID as a way to uniquely identify emails. If you have a question or concern about a specific email, Elastic Email Customer Success staff can use the MessageID to quickly look up details regarding your email.
There are a several ways you can locate an email's MessageID.
From Your Email Logs
Go to the "Activity" tab>Email log and click the "eye" icon besides an email. A popup will appear with email's details, including the MessageID:
Within the UI, you just click the "eye" icon on the email. The Email Viewer will display all details, including the MessageID. The same information is available in the exported Email Logs.
Directly from your Email Client
The MessageID is implemented in the email as a "header". You can display the MessageID of an email directly in your email client by viewing the "original" or "source" header. In emails sent via Elastic Email, the MessageID header is usually present as "X-msg-EID".
Google has a help document showing how to find this option in most email clients.