Yahoo will receive the IP address that your ISP (Internet Service Provider) has assigned to your account anytime you access a Yahoo webpage, you don't have to be signed in at all.
When you send email from any website, including Google's Gmail, your current IP address is included in your email headers, it's the way email is designed.
If you are at work or school or a library and send email from your Yahoo account, their IP address will be in the email headers.
Your computer has an IP address, but if it is connected to a router, the computer's IP address will not be the same as the IP address assigned by the ISP.
Your MAC address will not be sent out. It does not travel past the router.
BUT - if malware has gotten on your computer, the malware can read anything on your computer, and then send that information out to criminals who control the malware remotely. They can get your MAC address, the serial numbers from hard drives, they can read anything on your hard drive.
Generally speaking - no, it is not. The computer that sends the e-mail has full control on what it puts in the initial headers, so a rogue computer (or a rogue sender) can put there *anything*. However, the computers that receive the e-mail and forward it further until it reaches yours also add their own information to the headers - and that information is usually genuine. After some careful digging it is often possible to at least discover the first computer that has received the offending e-mail. Which computer it has received it from, however, usually requires access to the logs of the computer you have found, and that requires cooperation of its system administrator. Even then, it's a rather hopess task. The offending e-mail might have been sent from some free Web e-mail or mail forwarding site - or even from a "zombie" machine the attacker has control of while its owner has no clue what their machine is being used for.
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They can see your IP address.
Yahoo will receive the IP address that your ISP (Internet Service Provider) has assigned to your account anytime you access a Yahoo webpage, you don't have to be signed in at all.
When you send email from any website, including Google's Gmail, your current IP address is included in your email headers, it's the way email is designed.
If you are at work or school or a library and send email from your Yahoo account, their IP address will be in the email headers.
Your computer has an IP address, but if it is connected to a router, the computer's IP address will not be the same as the IP address assigned by the ISP.
Your MAC address will not be sent out. It does not travel past the router.
BUT - if malware has gotten on your computer, the malware can read anything on your computer, and then send that information out to criminals who control the malware remotely. They can get your MAC address, the serial numbers from hard drives, they can read anything on your hard drive.
Generally speaking - no, it is not. The computer that sends the e-mail has full control on what it puts in the initial headers, so a rogue computer (or a rogue sender) can put there *anything*. However, the computers that receive the e-mail and forward it further until it reaches yours also add their own information to the headers - and that information is usually genuine. After some careful digging it is often possible to at least discover the first computer that has received the offending e-mail. Which computer it has received it from, however, usually requires access to the logs of the computer you have found, and that requires cooperation of its system administrator. Even then, it's a rather hopess task. The offending e-mail might have been sent from some free Web e-mail or mail forwarding site - or even from a "zombie" machine the attacker has control of while its owner has no clue what their machine is being used for.
ANY email server legally HAS to attach the sender IP address.