It is very easy for spammer to fake your email address because "From address" is not restricted in SMTP protocol. It depends on the relay server (in most situation, the sender server) whether verify the from address before sending out. Many mail providers on market do not restrict this rule.
To reduce spoofing, you can perform follow precautions:
1. Set up SPF record for your email domains. SPF record tells the mail receiving server information about validity of sending servers. It specific which mail servers will send out email on behalf of your domain. (you can see setup instruction here)
2. Do NOT put your own domain as Trusted sender or White list. Otherwise your SPF may not work.
3. Avoid use common names such as sales, support, info, webmaster for email address. These common email address will have a high risk of being spamed and spoofed.
4. Avoid display your email address on your website via HTML. If you have your email address on your website, it'll get crawled by spambot easily. You should use an image instead. Create an image with your email address on it and then display it on your website.