Do in regards to and regarding to imply different meanings or is it okay to use them interchangeably?
This mail is in regards to your inquiry.
This mail is regarding to your inquiry.
I would say these are correct:
I honestly have never seen this use:
"In regards to" is a common error, but an error nonetheless. "In regard to" is correct. The "s" would be stuck onto "regard" only if you are saying "as regards," which is a correct alternative.
"With regard to" is also correct.
"Regarding to" is incorrect; "regarding" is all you need to say.