Outlook .msg vs .eml: what's the difference and which should you attach to a ticket?

What the two formats are

.eml is the email as it travelled: a plain-text file in the internet mail format (RFC 5322 with MIME). The headers are at the top exactly as the mail servers wrote them, the text and HTML body follow, and attachments and inline images are encoded inside. Any mail program can read it, and so can a text editor.

.msg is Outlook's own format, documented by Microsoft as MS-OXMSG. It stores the message as a set of Outlook properties rather than as internet mail: subject, sender, recipients, the body (often in Outlook's RTF form, sometimes only in that form), attachments, and, for a message that arrived over the internet, the received headers in one property. Outlook opens it with a double click; most other programs do not.

What each one keeps

• Headers. An .eml always has the full headers. A .msg has them only if the message came in over the internet and Outlook stored them; an email that never left the company's Exchange server, or a message you wrote yourself, usually has none. Without headers, nobody can check SPF, DKIM or DMARC or trace the route.
• Formatting and inline images. Both keep them. A .msg may hold the body only as RTF, which needs a viewer that understands Outlook's RTF.
• Attachments and nested emails. Both keep attachments, and both can contain another email inside.
• The file name. An .eml saved from Outlook on the web or from Gmail is named after the subject; a forwarded email can arrive on a ticket with no extension at all.

How to save an email as a file

Classic Outlook (Windows): drag the message from the list to a folder or onto the Jira work item for a .msg; or File, Save As, and choose the format.

New Outlook (Windows) and Outlook on the web: open the message, then the three-dot menu in the reading pane (More actions), Save as; the new Outlook offers .msg and .eml, Outlook on the web calls it Download.

Gmail: open the message, More (three dots), "Download message". That gives an .eml.

Apple Mail: File, Save As, set Format to "Raw Message Source". That gives an .eml.

Atlassian's own support team asks for .eml files when they need to analyse an email, for the same reason given below: the headers are in it.

Which to attach to a ticket

For evidence (a phishing report, a complaint, a legal or procurement thread): .eml. It is the message as sent, headers included, and any tool on any platform can read it. If you only have a .msg from Outlook, attach that; a .msg that arrived over the internet still carries the headers.

For convenience (an agent dragging a mail onto a ticket from classic Outlook): .msg is fine. It takes one drag, and the viewer apps for Jira handle it.

For a mixed team (Mac, web, Gmail users reading what Outlook users attached): prefer .eml, so nobody needs Outlook to open it.

Reading either one in Jira

Jira Cloud shows an .eml as raw text and a .msg as unreadable code; neither is readable on the work item. Free routes and viewer apps are compared in how to open .msg and .eml attachments in Jira. Full disclosure: Dortus makes such an app. MailView reads both formats on the work item up to 10 MB, including .msg files whose body is only RTF, forwarded emails attached without a file extension, and an email inside an email, and shows the headers with a plain-English verdict when they are there.

Short answers

Can I convert .msg to .eml? The new Outlook can save a message as .eml or .msg (More actions, Save as). In classic Outlook, Save As gives a .msg by default (Microsoft: Save an Outlook message as a .eml file, a PDF file, or as a draft). Converting after the fact does not add headers that the .msg never had.

Does Jira treat them differently? No. Both are attachments; Jira displays neither.

Questions

Not sure which format your desk should standardise on? Email support@dortus.com.

See also: How to attach an Outlook email to a Jira work item and How to open .msg and .eml attachments in Confluence