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bgmCoder
Asked: 2016-11-26 13:13:38 +0800 CST

External o365 Mail-Users Receive plaintext

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In my Office365 I have an Office365 Group. Whenever I add a Mail-User (external) to the group they receive the welcome message from the group, but it is in plaintext, complete with image file attachments and winmail.dat.

The message comes across like this:

Welcome to the Roadkill Cafe group.

[cid:office365_icon_orange]

[cid:group_photo.jpg] Roadkill Cafe Welcome to the Roadkill Cafe group.

Roadkill Cafe group

[cid:welcome_onenote_icon]https://outlook.office365.com/owa/[email protected]/groupsubscription.ashx?realm=roadkillcafe.com&source=WelcomeEmail&action=onenote Share noteshttps://outlook.office365.com/owa/[email protected]/groupsubscription.ashx?realm=roadkillcafe.com&source=WelcomeEmail&action=onenote

Capture ideas and images in OneNote.

[cid:document_icon]https://outlook.office365.com/owa/[email protected]/groupsubscription.ashx?realm=roadkillcafe.com&source=WelcomeEmail&action=files View and share fileshttps://outlook.office365.com/owa/[email protected]/groupsubscription.ashx?realm=roadkillcafe.com&source=WelcomeEmail&action=files

View, share, and collaborate on content using SharePoint.

I have tested this with my local email server and with Yahoo.

However, if I add one of the non-external users (licensed o365 user), the message is sent in html. Or, if in OWA, if I add a "guest" to the group who has a yahoo.com address, that person is also sent a normal html email like it should. I have also tested this with a gmail account.

So I added a remote domain under Exchange > mail flow > remote domains and configured that domain for Always use rich-text format (it was default set to follow user settings) and I changed the character sets to Western European. But this had no effect.

This MS help document says to make an adjustment that will force the message into plaintext and eliminate the winmamil.dat file altogether. However, I want the message to be in html, not plaintext. And besides that, none the three settings (Use rich-text format: Always, Never, Follow user settings) have any effect on the message at all.

How can I fix this?

[update]

Apparently, the mail-user receives ALL email correspondence in plaintext, not just the welcome message. This happens when you post anything in "conversation" in the group itself.

However, if I send an email to that same group, it is received as html! Go figure that. Post to the group directly and it sends plaintext; send an email to it and it sends html.

[update]

So I tried using powershell against the mail-user object like this, but this also did not change the welcome message to html:

set-mailuser -identity [email protected] -messageformat mime -messagebodyformat html
email microsoft-office-365

2 Answers

  1. Best Answer

    Well! I ended up making a Support Request through the Office365 interface. The Folks over there at the MS Service Center told me that they were able to reproduce the problem.

    Their solution? It seems that my tentant's server is one update-patch behind and that perhaps when that patch is applied (no idea of when) it might solve the problem. Or, if enough other people have the same complaint they will look into it more deeply.

    Such wonderful promises they make to me! In the meantime, I have decided to avoid adding mail-users to Office365 groups using the Office Admin web GUI. I shall have to do it in powershell and script out my own welcome email.

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  2. This fixed it:

    Set-RemoteDomain Default -TNEFEnabled $false

    Details: How to Fix Winmail Dat Attachment Issue

    The post is old, but I still got the same issue in 2020, and it is not well-explained by MS, hope my reply makes life easier for someone.

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