A new spammer tactics has been discovered by spammers nowadays...
They use 2-step factor by using both manual and auto tactics. Firstly they send an e-mail secondly waiting your reply and then re-post their scam pdf's, links , landing pages or e-mail contents ..
And these tactics is not mostly understandable by Google Spam Prevention.
These tactics mostly for fraud and scam/fake transactions for the targeting of webmasters online.
So, what are their tactics?
1-) They firstly send an email like this:
It is simply implied that they are inquiring your services, products etc.
2- ) If you send a reply to them, them return back to you immediately
If you reply their (spammers) e-mails they return back to you and then send you a file or link in order to get your details/passwords/website logins or payment gateway info's.
Note: These e-mails mostly cant recognize by Gmail's Spam Detection and most probably you can see these e-mails in your primary inbox.
So, in conclusion please do not care them and simply remove and take their emails to Gmail Spam Folder.