MailRaider

Have you got an .msg file that you can't open? Did you get a winmail.dat file instead of the message that you were expecting? MailRaider is the app for that.
MailRaider has been opening Microsoft email formats on Mac since 2009 — longer than any other tool on the App Store. The iOS version brings that same capability to iPhone and iPad, so you can deal with these files wherever you are, without needing to be at your desk.

What MailRaider opens:

.msg — Microsoft Outlook messages
.eml — standard email format
.oft — Outlook template files
winmail.dat — the mystery attachment that arrives instead of an actual email message

What you can do with them:

Read emails with full formatting, embedded images, and attachments intact
Export contacts to .vcf and calendar appointments to .ics
Play back voice note recordings and export transcripts
Search through your emails and browse folder structures
Import from iCloud Drive, Dropbox, Google Drive, OneDrive, directly from Mail - or copy over from your Mac or Windows PC.

On iPad: full multitasking support, including Split View and Slide Over. MailRaider is a proper iPad app, not a scaled-up iPhone app.
No subscription. No hidden costs. Pay once and that's it.
MailRaider on iOS is MailRaider — to go.