Spammer (noun)

1. A person or entity that sends unwanted or unsolicited electronic messages, typically in bulk.
2. A person or organization that uses electronic messaging to send unwanted or unsolicited messages.

Origin:

From spam (unwanted electronic message) + -er.

Examples:

1. The spammer sent out thousands of emails in a short period of time.
2. The spammer was trying to sell counterfeit goods.
3. The spammer"s emails were blocked by the email provider"s spam filter.
4. The spammer used botnet to send out the unwanted messages.
5. The spammer's activities were illegal under anti-spam laws.