When you need to create a line feed (new line) in a VBA text box you can do so in the string that you’re using to assemble your message using any one of a number of methods.
You can use Chr(13) which is an old style character conversion of ASCII character 13 which is the carriage return and line feed character. Or you can use vbNewLine or even vbCrLf.
But, try as you might, all you will get in your textbox is a silly paragraph marker and not a new line if you don’t set your textbox up as a multiline text box in its Properties. Don’t say I didn’t warn you!