Any way to block specific email (address(es)?

Hi, wondering is there any way to block a specific email address with gmail and/or yahoo mail?]

For example: if someone with the address, johnsmith@gmail.com sends me an email amd i don't want to be spammed by this person, can i enter the address "johnsmith@gmail.com" into somewhere telling gmail to refuse this address?
Hope you get what i mean

Thanks

Can't you just flag a mail received as spam and it will go straight to the Spam folder?

CCOVICH said:

Can't you just flag a mail received as spam and it will go straight to the Spam folder?

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yes but some of my "spam" is legit and i would rather just completely block an address than have to wade through tonnes of spam in order to find the legit ones like my broadband bills. Unless you can tell me if i can flag certain spam as proper email an get it sent to my inbox instead in future?