A friend of mine has just received an email from my exactly own email adrress. What could this be and how do I stop it?
Your email provider either has a relay open on an SMTP server or they don't use SPF or DKIM records to prevent mail from being sent as domains that use their domain name.
Another possibility is that the e-mail is not from your address but the display name of the sender has been set to your e-mail address. (
FROM: "email@example.com"<firstname.lastname@example.org>) This is more often the case and can create confusion for email recipients.
My advice would be to first determine if the email actually came from your email address or if it came from a fake email address using your real email address as a display name.
If the e-mail actually came from your address, look through the headers of the email your friend received to determine where it came from. You can also use the headers to check for DKIM and use online tools like DMARC Analyzer to check to see if your email provider's domain has an SPF record. If your provider does use DKIM and/or SPF and the e-mail did come from your address, then you may want to contact your provider to see if there are any issues with third-party mass-mailing vendors who have permission to send as your email address's domain.