The available properties of StringList are listed in the Formativ Language Guide, under Utilities.
I suggest using the Text property to append your string list, as in:
newMail.BodyText = newMail.BodyText & strList.Text
If you need to append more than one ‘chunk’ (or section) of text to BodyText, it is probably more efficient to progressively append the chunks to a string list (eg. strlist.Add). Then assign the resulting string list to BodyText:
strList.Add("Mary had a little lamb") strList.Add("whose fleece was white as snow.") newMail.BodyText = strList.Text
I hope this helps.