Spammers Check email address for activity

Dear, did you happen to have recently received a letter to the post with the following content?
- [beginning of letter] -
I would like to buy your site *******. ru
write the cost if you sell.
- [end of letter] -

Sender: pro.d [there are more letters here] sik@gmail.com

Do not respond in any way to this letter.
As already mentioned in many forums - this is how spammers check your mailbox for the fact that you have not abandoned it. That is, "live" or not.
Apparently, here alphabetic lists of registered domains are used, by which your email address is easily recognized and then a letter is drawn up from this data, in which the address of one of your registered domains appears (which seems to cause confidence).
Spammers do not yet drive in the name of the domain to which they are registered. But this is apparently temporary.

Be carefull!
')
Who cares : Google on this topic