Yes, the broader context of that email chain is a broad unloading of a 'greatest hits' of a decade of grievances against SparkFun (the meme site mentioned was made in 2017, by an employee who no longer works there).

I quoted the lines that seemed to most obviously tip that particular email exchange beyond a measured harassment report (as originally implied), crossing the line into what could be reasonably considered 'unappropriately aggressive behavior' (to quote the SparkFun CoC).

I would agree that the ex-employee's 'Sincerely, Fuck Off' was similarly aggressive, but less relevant since he's no longer an employee anyway, and it seemed pretty clear that he was the one being subject to targeted harassment in this instance (having accusations being forwarded to his partner's employer) rather than the other way around.