Question

I have never sent an attachment, too/also/either.

Answer 1

I have never sent an attachment too.

Answer 2

You can use "either" in your sentence to convey that you haven't sent an attachment, just like someone else also hasn't sent one. Here's the sentence with "either":

"I have never sent an attachment, and I haven't received one either."

In this context, "either" emphasizes that neither you nor someone else has sent an attachment.