DotNetNuke.Services.Mail::sendMail doesn't use bodyEncoding for alternative view in multipart message

[tingung]

Description of bug

DotNetNuke.Services.Mail::sendMail doesn't use bodyEncoding for alternative view in multipart message. Emails are sent as ASCII but whenever a special character such as \n or \r is included the content type becomes UTF-8.

Steps to reproduce

List the steps to reproduce the behavior:
Create a Simple Email module

1. Go to a page > Add Module > Module Creator
2. For the View.ascx.cs, put in the sendmail method with ASCII encoding in the button event.
3. Mail.SendMail("from@local.me", "", "test@local.me", "", 0, "", 0, Encoding.ASCII, "body\n", "", "", "", "", "");
4. Save the module. Save the field to send email and observe the email received. Check the email's Content-Type.
5. Change the the "body\n" to "body". Save the module. Save the field to send email and observe the email received. Check the email's Content-Type.

Current result

Email with body - "body\n" Content-Type received is text/plain; charset=utf-8
Email with body - "body" Content-Type received is text/plain; charset=us-ascii

Expected result

Email's Content-Type charset should always consistent with encoding. If encoding is set to Encoding.ASCII, then charset should always ascii in
regardless the body content

Screenshots

https://www.loom.com/share/b9ebd96afcbf4070be17c063e7326752 - video recording

Error log

Nope

Additional context

Dnn.Platform/DNN Platform/Library/Services/Mail/Mail.cs

Line 109 in 584b0f5

var PlainView = AlternateView.CreateAlternateViewFromString(ConvertToText(body), null, "text/plain");

- the problem is
the encoding is set to null. We shall set the encoding with the bodyEncoding

Affected version

• 9.3.2
• 9.3.1
• 9.2.2
• 9.2.1
• 9.2
• 9.1.1
• 9.1
• 9.0

Affected browser

Browser independent issue

• Chrome
• Firefox
• Safari
• Internet Explorer
• Edge

[mitchelsellers]

Due to branching changes, this change needs to be re-evaluated to see if it is needed for the 10.x release. If so, the changes from PR #2900 will need to be replayed against the new 10.x branch.