Reply/Forward Sent email issue.
case 1:
I start new email and send it out after I reply/forward this email from sent folder and no any format problem.
case 2:
I reply/forward a email in "New Mail" folder after I reply/foward thie email from sent folder and I got some format issue in this email...this will show "?" into "space", something like that:

---
From:        xx@xxx.com
To:          xxx@xxx.com
Copies to:   xxxx@xxxx.com
Subject:     Re: xxxxx
Date sent:   Web, 26 Jul 2023

Hi,

This is a test 2.

Regards,
Buyer
---
From:xxx@xxx.com
To:xx@xx.com,
????????"xxxx" <xxxx@xxxx.com>,
Subject:xxxxx

Hi,
?
?
This is a test 1.
?
?
Regards,
Buyer
?

I also hope you can fix this issue.

Regards,
Buyer

Not that I would understand what you're doing there, but what's your setting on Tools > Options > Advanced settings > Default MIME character set? UTF-8 would be recommended.

Regards,
Buyer

I struggling to understand what you are doing and what it happening so let me make some comments in the hopes that one of them will be of value.

First, I don't understand why you would ever reply to a copy-to-self so I am going to assume you are talking about a forward, or perhaps a resend.

Comment 1:
When doing a forward, if you select the option "Edit or make changes to the message...", the body of the message will include the headers of the source message. That is by design. They can be removed if you want.

Comment 2:
A copy-to-self version of a message was originally designed solely as a record. It did not maintain attachments or images. The 4.81 beta version has expanded that to include the following copy-to-self format options:

• Reloadable (the current standard): Able to be reloaded and re-sent.
• Final form: Not as reloadable, but a more accurate representation of what the recipient would see, including attachments and pasted graphics.
• Both: Two copies to self are made, one in the reloadable form, the other, displayed in a pale blue colour, in the final form.

Perhaps the Final Form version would be suitable to your needs.

Make sure to enable formatting options on Tools > Options > Message formatting, i.e. don't check any of the options shown there which would disable them. Since I don't have your samples available I took a spam message containing Chinese characters and it appears to work: Formatting will take care of font settings to be properly carried over to new messages.

PS: And enable For replies to HTML, preserve original's formatting in Pegasus Mail's reply options dialog so it will do the same with forwarded messages as well. If you don't do all of this, you might still see everything in formatted style in your editor but the outgoing message might not keep the formatting anymore. And what I don't know is whether this would work with plain text messages at all no matter at which point they come into play.