Outlook on the Web's language settings are in English, but the character encoding becomes Chinese
Conclusion
Set the display language of your client to Japanese.
How I found the Issue
I regularly use Outlook on the Web (formerly known as Outlook Web App), but recently, a recipient of my email told me that the email was garbled(mojibake).
Upon checking the email header, I found that the character encoding had somehow been set to Chinese gb2312.
This kind of issue hadn’t occurred in the past few years, but on November 20, 2024, a friends told me about this issue.
Cause
The root cause of the garbling was this character encoding.
The problem was that the emails I sent were encoded in Chinese gb2312.
When sending emails to Gmail accounts, they were delivered without garbling, even with gb2312 encoding. However, emails sent to other internet providers resulted in garbled text.
The email subject and body I sent contained a mix of Japanese characters and half-width alphanumeric characters.
The reason for this issue turned out to be that my display language in Outlook on the Web was set to English.
My display language had always been set to English, but I had never received any complaints about garbled text in the past.
Resolution
Changing the display language to Japanese caused the character encoding to switch to iso-2022-jp, which is suitable for Japanese. This resolved the garbling issue.
Why Not UTF-8?
I initially thought that switching to utf-8 would solve the issue entirely. However, Outlook on the Web doesn’t have a menu to set character encoding.
The new Outlook for Windows, known as Outlook (new), also lacks a menu for setting character encoding. In fact, the new Outlook for Windows seems to operate similarly to Outlook on the Web.
I tried changing the character encoding to utf-8 via the Remote Domain settings in the Exchange admin center, but the emails still weren’t encoded in utf-8.
Other Tests
Setting the language to English (World) and sending an email with only alphanumeric characters
In this case, the charset was set to us-ascii.
However, when Japanese characters were included, the charset changed to gb2312.
Setting the language to English (United States) and sending an email with only alphanumeric characters
In this case, the charset was set to iso-8859-1.
However, when Japanese characters were included, the charset changed to gb2312.
Setting the language to Japanese and sending an email with only alphanumeric characters
In this case, the charset was set to us-ascii.
When Japanese characters were included, the charset changed to iso-2022-jp.
Outlook, please let us use UTF-8.
