There is so many potential things that could be happening here.
The attack may try phishing by you clicking an malicious link which would be related to malware such as keylogger or so on. The attack could also try social engineering so gathering all information he/she can about you then attempting to get into your account. Keep in mind the most e-mail servers will include the originating IP when sending e-mail so they could get your IP and attempt to hack into your computer. The spammer maybe just gathering active e-mail to send spam later down the line. 

 - [phising](https://en.wikipedia.org/wiki/Phishing)
 - [social engineering](https://en.wikipedia.org/wiki/Social_engineering_%28security%29)