Microsoft does have a figurative trademark for "Office" with the rectangular icon: https://euipo.europa.eu/eSearch/#details/trademarks/01141355... - office.eu's logo does not bear any resemblance.
The only way this would be infringing is if office.eu usage could be confused with Microsoft other's trademarks - like Microsoft Office - but I don't see that.
So no, office.eu will have a calm Monday on that front, just like hundreds of other companies offering products with "Office" in their name.
(I'm not a lawyer. Talk to a lawyer before deciding to take on a trillion dollar company).