I get the same behavior in Firefox 61.0.1 (64-bit) on Windows 10 Version 10.0.17134.167.

I do not see this problem using these browsers on the same Windows 10 Version 10.0.17134.167 workstation:

• Microsoft Edge 42.17134.1.0
• Chrome 67.0.3396.99

When the email is NOT displayed, the email window contains the following text in various sizes and colors:

expand_more
lock_outline lock_outline

collections
This message contains external images. close

message

The sender of this message has asked to be notified when you read this message. Do you wish to notify the sender?

[edit]
I seem to see this behavior only on systems that are frequently used to access webmail. On another computer that is used only infrequently, message display is working as expected (Windows 10.0.17134.16 / Firefox 61.0.1 (64-bit))

We had the same problem, please delete your Browser cache and try it again.

Clearing my browser cache did not solve the problem.

Here's what I did to clear my cache:

• Preferences -> Privacy & Security -> History -> Clear History -> Everything -> Check all items -> Clear Now
• Preferences -> Privacy & Security -> Cookies and Site Data -> Clear Data -> Clear

I've also tried:

• Help -> Restart with Addons disabled
• about:config -> general.useragent.override -> "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36"

Add the sogo page as trusted page (HTTPS) in the Internet Explorer settings.
You can find it under "Control Panel", "Internet options", "Security", "Trusted sides" and then you have to click on "Sites".
Restart Mozilla and it should work.

I added the sogo host as a trusted site in Internet Explorer on my failing Windows system (I could not figure out how to do the same thing on my macbook).

The problem did not go away.

The problem seems to be specific to my hosting configuration. As such I am happy for this issue to be closed.

DETAILS -

My two failing browsers both use an etherpad page as a bookmarking tool.

If I click on the SOGo link on my etherpad page, message bodies are not displayed.

If I open a new tab and load the same URL that did not work from etherpad, message bodies are displayed as expected.

Here are some apache log entries from failing and working sessions in case the developers feel differently -

Failing Session:
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /sogo HTTP/1.1" 302 217 "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /SOGo HTTP/1.1" 302 - "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /SOGo/mmccarn HTTP/1.1" 302 - "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /SOGo/mmccarn/view HTTP/1.1" 302 - "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /SOGo/so/mmccarn/Mail HTTP/1.1" 302 - "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:07:58:51 -0400] "GET /SOGo/so/mmccarn/Mail/view HTTP/1.1" 200 19362 "https://etherpad.obfuscated.us/p/office9" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"

Working Session:
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /sogo HTTP/1.1" 302 217 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /SOGo HTTP/1.1" 302 - "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /SOGo/mmccarn HTTP/1.1" 302 - "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /SOGo/mmccarn/view HTTP/1.1" 302 - "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /SOGo/so/mmccarn/Mail HTTP/1.1" 302 - "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:03:42 -0400] "GET /SOGo/so/mmccarn/Mail/view HTTP/1.1" 200 19362 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"

Working session (url added to https://httpd.apache.org/docs/1.3/logs.html using developer tools):
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:13 -0400] "GET /sogo HTTP/1.1" 302 217 "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:13 -0400] "GET /SOGo HTTP/1.1" 302 - "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:13 -0400] "GET /SOGo/mmccarn HTTP/1.1" 302 - "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:14 -0400] "GET /SOGo/mmccarn/view HTTP/1.1" 302 - "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:14 -0400] "GET /SOGo/so/mmccarn/Mail HTTP/1.1" 302 - "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"
obfuscated.us 192.168.200.110 - - [31/Jul/2018:08:21:14 -0400] "GET /SOGo/so/mmccarn/Mail/view HTTP/1.1" 200 19362 "https://httpd.apache.org/docs/1.3/logs.html" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:61.0) Gecko/20100101 Firefox/61.0"