Email spoofing is when the email header's "From" line is modified to something other than the actual sender. This is often exploited by spammers in attempts to trick the recipient into thinking the spam is from a trusted source such as an email address that they recognize.
Unfortunately, it's not possible to stop someone from using your email address as the from address. The reason for this is that the from address on an email works similarly to a physically mailed letter or package. You can put any from address on a letter sent using your community postal service. The post office does not check if the return address is indeed who sent the letter. It is similar with email.
While it's not possible to stop someone from using your email address as the from address, we can help the recipient of the spam detect spoofed emails and handle them accordingly (such as putting it into Junk E-mail folder). This is done using Sender Policy Framework (SPF). SPF record is a DNS entry for your domain that specifies the SMTP server(s) that are allowed to send email from your domain. So when spammers send an email from their own server using your email address as the from address, the receiving server can check the SPF and detect that the email is coming from a server that's not permitted to send email from your domain.
SPF records are created by default for all of our hosting plans that use our name servers.
Our spam filters also check for SPF records for incoming mail and will put them into the Webmail Junk E-mail folder if the email fails SPF check.