Hi @Hung-Jie Tsai ,
Welcome to our forum!
Terminal computer outlook version has 2010 ~ O365 all have
Do you mean that this problem occurs in all versions of Outlook client? Maybe the problem happened in one of the versions of Outlook?
For the "some emails" you mentioned, what do they have in common? For example, to some specific recipients? Or something else?
According to your description, I noticed that after the recipient opened the forwarded email, he saw that the email was garbled. To further confirm whether the problem is related to the recipient's computer, please check whether the forwarded messages in the sender's Sent Item folder are garbled.
Considering the impact of language inconsistency, is the language of your current computer the same as that of outlook client, as well as the languages of sender and recipient? If not, it is recommended to set the language to the same language.
In addition, we can usually avoid the impact of some add INS by starting outlook in safe mode. It's suggest you try to do the same test on the problem emails in safe mode(Windows + R> type "outlook.exe /safe">enter) to check whether it is different.
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