Is it correct to use the following sentence part
As my friend already introduced, ...
when I want to express something like
As my friend has already communicated to you, ...
with ... being some fact my friend has sent in an earlier email.
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This would depend mainly on the context.
While not incorrect, consider the terms "mentioned," "explained," "already mentioned," or "already explained" in the place of "introduced." If none of these options are preferred, "introduced" should be acceptable.