My husband is Pakistani but was living and working in Spain. He received an email such as yours. We responded the day he got it. It took another 2 years AND a stokes interview that involved both of us in Madrid. Luckily I was there when they requested us both to go to the embassy.
It is the ds 5535 but in an informal email.
Good luck with your journey, it won't be quick. Just saying the truth.