Are you asking because you don't want to share your current salary? (Maybe you want/expect a lot more than you currently get.)
Are you asking because you want to share, but don't know if you are allowed?
1. If your current company/employer is private, then the salary information could be considered a "trade secret", "confidential" or at least you don't know that it is "public". So, you might not legally be able to tell them. Or you might be able to use that as an excuse to not tell them.
2. In particular, if you are looking for a large increase and don't want to anchor them at your current salary: Salary is only one portion of compensation. I know people who got HUGE salary increases when leaving one employer with great benefits for one with weaker benefits. (Benefits are not just financial, as they can include telework, training, work/life balance, guest speakers, conferences, etc.) There are also geographical differences in salary.
3. For the "email" portion. That is a better question for the "security" group, which would likely tell you not to do that, however, everyone does, even those in "security".
4. If you are asking about how to get the best offer: Most discussions, like many on LinkedIn or Ladders state that you should tell them that you expect a competitive salary and total compensation, based on current market conditions; and that salary amount is between $x and $y, depending on the benefits. Make $y just a bit higher than what you expect as an "anchor". They'll likely offer a little less than $x, if both of you have done your homework and know the market.