Spam sent from my email address A relative told me that he received an email from me this morning, that arrived in his spam folder. He opened it and apparently there was some porn related things inside. Obviously, I didn't send this email, and it doesn't appear in my sent message.

What also surprised me is that apparently, another of my contacts was also in CC, even though these 2 persons know each other and probably have each other's email in their contact list.

Sadly I don't know more about the email itself, if it was my real address that was used or simply something like "John Doe &lt;spam@email.com&gt;"

My email (@icloud.com) is only setup in the Mail app of my Mac and iPhone. When reading my mails from a browser, I have 2-step authentication activated, so I can't have been hacked.

I'm not familiar with this kind of spam, so I have a few questions:


Could it be sent from my Mac? I had the (perhaps wrong) idea that Mac were less prone to this kind of annoyance than Windows computer.
If not my Mac, then could it possibly be my iPhone?
Is there an efficient way to protect yourself against this kind of spam? I already have an antivirus installed on my Mac, and I make sure never to install anything from untrusted source.
It is unlikely either your Mac or iPhone was used to send the e-mail. Regrettably it is difficult to protect yourself from this problem.

See Receiving spam from myself for a related question and answers about this subject. For a more technical overview, start with this spoof email search of the StackExchange network.

Spoofed E-mails

How Spammers Spoof Your Email Address (and How to Protect Yourself) – article from LifeHacks in 2014 helps explain the sitation:


  Most of us know spam when we see it, but seeing a strange email from a friend—or worse, from ourselves—in our inbox is pretty disconcerting. If you've seen an email that looks like it's from a friend, it doesn't mean they've been hacked. Spammers spoof those addresses all the time, and it's not hard to do. Here's how they do it, and how you can protect yourself.
  
  Spammers have been spoofing email addresses for a long time. Years ago, they used to get contact lists from malware-infected PCs. Today's data thieves choose their targets carefully, and phish them with messages that look like they came from friends, trustworthy sources, or even their own account.