The correct answer is "in regard to". Even better, "this is regarding ..."
Don't forget that "regards" usually means an expression of sentiment something like "best wishes", as in, "Please pass along my regards to your father." or, as in the old musical number, "Give my regards to old Broadway!"
According to the Dr. Grammar site:
In regard(s) to?
"The use of the plural regards in the phrases in regards to and with regards to is incorrect. Since each phrase shows its speaker regarding just one issue, the regard is singular: in regard to and with regard to.
[Examples:] I am calling in regard to your memo.
With regard to our meeting, I cannot attend." (Strumpf and Douglas, The Grammar Bible 220).