How do spammers get my email address?

Spammers harvest email addresses in many ways. For example:

By searching. They use specialized search engines (Spambots) to collect email addresses from web pages, newsgroups, bulletin boards, discussion forums, white & yellow pages, mailing lists, ... etc. automatically.
By guessing. They can generate a random sequence of characters, hoping to match a few valid addresses.
By purchasing. They can buy or exchange email addresses from other spammers.
By having access to some persons' computers through Trojan viruses
By social engineering. Spammers use a hoax to convince people into giving their email addresses.
People may be required to submit their email addresses on the Internet (e.g. before downloading some software), and these email addresses may be released to unknown persons.
People may leave their email addresses in some dubious questionnaire that are found on the Internet, on the street or on telephone.

You can refer to the external references for more information

External references: How do spammers harvest email addresses

IT.ServiceDesk@cityu.edu.hk