How to sum this for sum number with @ in attach?

a little clunky but this will get you there...
=SUM(IFERROR(--MID(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1,","," "),"@"," ")," ",REPT(" ",100)),ROW(INDIRECT("1:20"))*100-99,100),))

for my version of excel it doesn't need to be an array but for earlier versions - likely yours, you may need to make it an array formula.
if you are not familiar with array formulas, while your cursor is in the formula in the window, you hit the ctrl+shift+enter buttons at the same time so that {} appears at either end of the formula. YOU CANNOT add them yourself, so it can be tricky if you haven't used an array formula before trying to get them to appear, it could take a couple attempts.

You're welcome, glad I could help, AND thank you for the rep!