Forum Discussion
How to Block a domain that has hyphen in the name in O365
How to Block a domain that has hyphen in the name in O365
There's nothing special about domains with hyphens, you can add it to the spam block list just as any other domain.
VasilMichevBlocking using the Spam section of 365 doesn't block, it just files to the quarantine meaning an email from a domain that you've "Blocked" still needs to be reviewed and dealt with. The only way (I've found anyway) to actually BLOCK a domain is to use transport rules. Transport Rules don't like hyphens.
I can imagine this is what the OP is referring to.