Yes this is a common feature of spam emails. It is easy for spammers to send emails to one account with the address of another account in the "To:" field.
How I deal with this.
1] I NEVER open these emails. I delete them immediately. Opening a spam email can send a message back to the spammer that your email address is current and active. A bonus for such spammers as they can send you more spam.
2] I NEVER Preview these emails. That is the same as opening them and so see above. What do I mean by Preview? Outlook, as well as other email software, like Thunderbird and so on, will list emails in your Inbox and this list is displayed in the right hand pane. These email clients can also display a Preview pane below this list which, when an email is highlighted, will preview the email in this pane. Previewing an email is the same as opening it, so when I see a suspicious email I turn off the Preview pane. On my Thunderbird that can be done in View > Layout > Message Pane, (or Preview Pane). I then highlight the email and delete it, and only then do I turn the Preview pane back on. Your Outlook will have a similar option.
I have also learned a trick. If my Inbox is empty and the next email I receive is a spam email, it highlights automatically and so displays in the Preview pane straight away. To avoid that I sent myself an email. I called it Test and when received I left it at the top of the Inbox listing. That way, every time I open my email software this test email is the first to display, and that allows me to look down the list, identify spam, remove the Preview pane and delete the offending emails.
3] If I do open a spam email in error, I Do Not click any links in the email, and I Do Not attempt to click any "Unsubscribe" to the email. Either of those will send a message back to the spammers telling them I am ripe for more spam emails.
4] I have set up extensive rules to remove emails from my Inbox if I don't want them. For example, anyone who sends me an email who is not in my address book or contacts list gets removed to a Junk folder.
5] I NEVER post my email address in public forums like these. Forum robots, (bots), trawl forums like these for posted email addresses so they can be spammed.
These emails you are receiving will eventually die down if you can follow those guidelines.
I hope that helps.
For the last year now I receive mail but instead of firstname.lastname@example.org, for example, WHICH IS MY EMAIL ADDRESS, I receive positively spam mail with my address portrayed as email@example.com,numerous mails from numerous people each using a different username. This annoys me very much because people can use any username and their garbage ends up in my mailbox. Please help