Functionality for Viewing .eml and .msg Files

[jakerogers-1]

Most email clients save email chains as .eml, .msg, or both, but most applications are unable to open these, meaning the user has to open a full email client to read them. I think it would be really useful to integrate these file types into a document viewer such as Sumatra. It would make reading emails much more convenient, especially when the email chains are quite long.

I think it could also help with providing emails as proof or evidence which is required in a lot of business, government, and academic contexts. In these situations, proof is often required as a document or image even though most email clients don't export in those file formats. But in Sumatra reader, the print to PDF feature allows for exporting documents as a PDF.

Together this makes for a really simple way to read .eml and .msg files and to then export them as a PDF for use in various places.

If this sounds like a useful feature and if you wouldn't mind, I would gladly work on a turning it into a pull request.

Thank you!

[GitHubRulesOK]

There are differences in the 2 mail formats so there may be limited similarities in MuPDF has a docx viewer
However SumatraPDF traditionally has not included such office biased formats.
IF accepted by the developer (which I am not) it adds to the maintenance of more formats and currently there are other related format issues to resolve first, such as CSS and scaling.

[jakerogers-1]

That's a good point. It's true that .msg is office biased but as far as I'm aware .eml is quite general and used by numerous email clients, some unrelated to office. It follows the MIME standard which is mature and unlikely to be updated very often, so in this case, I think maintenance wouldn't be too laborious.

[GitHubRulesOK]

EML is simple text with embeded base64 thus easy for Widows to use subsidary functions here seen in wordpad but the base 64 is not decoded as outlook has that ability
Although they read text files the eml is rejected by MuPDF and SumatraPDF

Usually a lot of dialog work is needed for all the relevant fields

[jakerogers-1]

Would it be quite simple to write a parser that allows for the plain text components of EML to be displayed on Sumatra? Similar to how .txt or .html files are handled

[GitHubRulesOK]

The message would need the imbedded images and other attachments sliced as "paragraphs" and run through the windows b64 utilities such as certutil to convert into pictures and attachments etc then a lot of other fiddling.

The logical way is to convert the eml into a proper html page using weblike JS atob (ascii to binary) so the basic page would become like a HTML email similar to the one shown above since fields are easy to wrap as <div>isions around a string of text. I "guess" somebody should have done that somewhere.

The 2 big challenges then are can SumatraPDF see such an HTML file (there may be an issue there)
and how to hook that file opening conversion into the open html file function.

So as to avoid the HTML file issue Currently SumatraPDF can use roughly A5 size XHTML pages (ebooks), thus the first test is hand convert a small eml with inline pictures into such a format and test for capability to renders such a sized page.
I have shown elsewhere what such a file needs in terms of some methods
see https://superuser.com/a/1869911/1769247
the scripting just to alter a page size can be unusually long see
https://superuser.com/a/1863755/1769247

[GitHubRulesOK]

At a basic level SumatraPDF can read the EML if renamed to txt or htm but the embedded attachment of html needs conversion from text to binary html that step is relatively simple but would need a dedicated conversion and many attachments are then not viewable inside SumatraPDF such as XLSX or other office based zip files except as plain xml

[kjk]

No plans to add that.

[shubhamsinghsys24-hue]

I would definitely find this useful.

I work with archived emails quite frequently, especially when reviewing project documentation, legal communications, and historical records that have been shared as .EML or .MSG files. One of the biggest frustrations is that these files are often treated as "email client only" formats, even though in many cases users simply need to read the content, search through it, or save it as a PDF for documentation purposes.

In one particular project, I received several hundred MSG files from an Outlook archive that needed to be reviewed and included as supporting evidence in a compliance audit. Since not everyone on the team had Outlook installed, accessing the files became an unnecessary hurdle. We ended up using SysTools MSG Viewer Pro because it allowed us to open the MSG files directly, review attachments, search within the emails, and export the relevant messages to PDF for record-keeping.

That experience made me realize how useful native support would be in a lightweight document viewer. Most people aren't looking to manage mailboxes or send emails—they simply want to open the file, read it, search it, and possibly print or convert it.

Supporting EML and MSG formats would make tools like Sumatra much more valuable for legal, academic, government, and business users who regularly receive email records outside of a traditional email client.

I think the PDF export use case you mentioned is particularly compelling because email messages are increasingly being used as supporting documentation, yet many users don't have a straightforward way to view and preserve them.

[GitHubRulesOK]

@shubhamsinghsys24-hue
the long closed issue was stated in 2015 in answer to #363 and has been restated 2025 above.

NOT a "planed format" but then again if MuPDF was an email reader/writer SumatraPDF might follow.