Like others, I mind but wouldn't email. That's really ungracious. And now you feel bad, which you shouldn't, because people do this ALL the time, and in it's one of those things non-name-changers just have to learn to live with.
To me it's like repeatedly being called Mrs White if my name were Mrs Brown. It's as though the person is saying "Oh, close enough; I don't really care what her name actually is." Basically I'm being called someone else's name.
And while it may be a matter of "oh sod it I can't be bothered to write out 2 surnames" it can come across as something mildly aggressive, like "Well I think it's ridiculous that women keep their maiden names, so I'm going to ignore it whenever it happens."
My parents, for a long time, insisted on changing my name to my husband's. This caused practical problems. Once they sent me a package and I wasn't able to claim it from the post office because my identification (passport, license et al) has my name, not my husband's. And my father once bought me an airline ticket to come see him, and put it in my husband's surnname. It was a generous gesture, but it was post 9/11 and I wasn't allowed to get on the plane. Well, EVENTUALLY they let me on the plane, but only after the ticket was reissued with a surcharge.
In Spain, so far as I know, everyone's name is essentially double-barrelled. So there's a culture where you just get used to writing a lot of surnames. So it can be done!