Yes, your attempt is pretty right, but you also can say: Журнал отправляется\отсылается мне по почте\почтой.

No, this is not correct, it is acceptable and understandable but non-Russian. I would not say so, I would say "мне журнал посылают по почте" (мне [3 - dative] журнал [4 - accusative] посылают по почте). The passive voice is not used in Russian so often because there are a lot of cases (6) in Russian: Студенты (1 - nominative) спрашивают - The students ask / are asking, but Студентов (4 - accusative) спрашивают - The students are asked / are being asked. Я рисую - меня рисуют (I paint - I am painted). Они рисуют - их рисуют (They paint - They are painted).

If you took out a subscription to a journal that is sent to you by post, in Russian your phrase sounds like this: «Этот журнал приходит мне по почте» or «Этот журнал я получаю по почте». As to me, the phrase: «Журнал посылается мне почтой» doesn't sound natural, but anyway it's correct to say like that. But I wouldn't say that way. How the passive voice works in Russian: Martin is helped by Ivan. – Мартину помогает Иван. Martin was helped by Ivan. – Мартину помог Иван. Martin will be helped by Ivan. – Мартину поможет Иван. Martin is being helped by Ivan. – Мартину помогает Иван. Martin was being helped by Ivan. – Мартину помогал Иван. Martin has been helped by Ivan. – Мартину помог Иван. Martin had been helped by Ivan before something happened. – Мартину помогал Иван, пока что-то не случилось. Martin will have been helped by Ivan. – Мартину поможет Иван.

If you have subscribed to a journal that is send to you by post, then it should sound like this: «Этот журнал я получаю по почте/этот журнал мне приходит по почте». These are the only natural ways of saying your phrase, I think. You have to use my phrases, because all the other variants that you've been told don't sound natural at all! Here are some examples: Cotton is grown in Egypt – хлопок выращивается в Египте. His book hasn't been published yet – его книга ещё не опубликована. His house was built a year ago – его дом был построен год. This building will be demolished next mount – это здание будет снесено в следующем месяце.

So many answers already, but here's my take on it. The passive voice in Russian mostly occurs in cases when the focus is on the action, not on the object of the action. Legal/official documents can contain quite a lot of passive voice, and some phrases like "мне кажется", "ему нравится", "тебе снится", "как это делается?". In your sentence, the focus is on the object, not on the action. So it's more natural to say "Журналы мне присылают по почте/доставляют почтой", or "Я получаю журналы по почте", or "Журналы мне приходят почтой".