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To send body of email in UNICODE, you have to modify ASCII text.
Attached is an example project for Hebrew language. You have to modify it by use the same idea.
Subroutine detects, if current character is in Hebrew language – range of Hebrew letters is 224 to 250.
*Unicode code page Windows-1255 on Wikipedia : https://en.wikipedia.org/wiki/Windows-1255
To encode Russian, you have to change range to 192 to 255. May be, you have to include additional sub-ranges
*Unicode code page Windows-1251 on Wikipedia : https://en.wikipedia.org/wiki/Windows-1251
For Hebrew language used prefix 0x05. For example, letter in 240 in position 240 in Hebrew encoded as 0x05E0.
For Hebrew language used prefix 0x04. Russian letter in position 240 is encoded as 0x0440.
In your project you have to replace:
Replace ֙ for ҙ
*It seems like your HTML variant.
In common, you can store strings in String Library as ASCII, and convert text in temporary buffer to UNICODE/HTML.
Test and tell us if email with Russian (or other language) in email body is sent right or not.
If you still you having any further questions or concerns, please do not hesitate to contact us.