How can someone send spam that appears to come from my own e-mail address?

Any one can put your address in the FROM name slot so when you receive it it appears as if it is coming from you...In addition, if your account has been hacked it could also end up in your inbox. If you hover your pointer over that address it should display the actual address/site it came from. If it shows yours then you probably have been hacked....If it has not just delete the message. if you spam it you will not receive emails in your inbox when you place you address in the header prior to sending...IE: the CC or BCC line.

How can you tell if your account has been hacked

https://help.yahoo.com/kb/yahoo-account/SLN2090.ht...

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SECURING A HACKED ACCOUNT

https://help.yahoo.com/kb/mail/SLN3516.html?impres...

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REPORT A HACKED ACCOUNT TO YAHOO

https://help.yahoo.com/kb/SLN3402.html?impressions...

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My account is sending spam

https://help.yahoo.com/kb/yahoo-account/SLN2068.ht...

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ACCOUNT KEEPS SENDING SPAM

https://help.yahoo.com/kb/yahoo-account/SLN2159.ht...

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RECOVERING A LOST/FORGOTTEN PASSWORD

https://help.yahoo.com/kb/index?page=content&id=SL...

Also, when answering the security questions, if the

questions are changed by the hacker, you will have

an option to choose the previous set of questions.

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HAS YOUR PASSWORD BEEN LEAKED

http://news.yahoo.com/website-tells-passwords-leak...

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Do not have access to your alternate email or mobile number anymore

https://io.help.yahoo.com/contact/index?locale=en_...

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When users do not have access to their Yahoo account,

they are able to provide a different email address on

that contact form above. Yahoo Customer Care agents

would then have the ability to verify the correct owner

of an account and assist with securing the account.

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SAFEGUARDING YOUR YAHOO ACCOUNT

https://help.yahoo.com/kb/index?page=content&id=SL...

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Once your question has been posted for at least 1 hour

and has at least one answer click on 'Award Best Answer'

button next to your chosen answer.

Occasionally I receive e-mails with my own e-mail address in the 'from' box, though my e-mail account hasn't been hacked, so it hasn't been sent from my account. How is it possible?