In this question: " You always wrote by e-mail?", Why not use " Did" ?
Did you always write by e-mail?
I didn't undestand! Please, helping me!
Thanks

"You always wrote by e-mail?" is the informal way to ask .

"Did you always write by e-mail?" is the formal way to ask.

Rodrigo,
So, I can speak without the " Did" in Informal way? Is it correct? Thanks for help me

Yes, It's correct. But just in an informal situation like talking with friends, etc. In a situation like a job interview you will have to use the formal way to speak. But remember: Talking with friends doesn't mean that you will always have to speak in the informal way, you can use both: Formal and Informal.

And You're welcome!!!!!!

Thanks Rodrigo! :)

I don't think this has anything to do with formal/informal language...

"You always wrote by email?" is a statement made into a question (by changing the tone), which means the speaker is asking someone to confirm their suspicion.

"Did you always write by email?" is simply asking the same question, but without the speaker adding their own assumption.

Both are suitable in formal and informal situations.

Ok! LFJ, thanks for your answer!