Is the word postais the same in Brazilian and European Portuguese?

No

The difference lies in typical usage. In Continental Portuguese, "postais" is the standard plural noun for "postcards." In Brazilian Portuguese, while the word "postal" exists, it is rarely used as a noun to refer to the physical object; instead, Brazilians use the term cartão-postal (singular) or cartões-postais (plural). In Brazil, "postal" is primarily used as an adjective to describe things related to the mail service (e.g., código postal or serviço postal).

Brazilian Portuguese Examples

Note: In Brazil, "postais" is used as an adjective, and "cartões-postais" is used for the noun.

1. Eu comprei vários cartões-postais para minha mãe. (I bought several postcards for my mother.)
2. O sistema postal do Brasil é muito grande. (The postal system of Brazil is very large.)
3. Ela gosta de colecionar cartões-postais de viagem. (She likes to collect travel postcards.)
4. Verifique o seu código postal no formulário. (Check your postal code on the form.)
5. Mandei um cartão-postal do Rio de Janeiro. (I sent a postcard from Rio de Janeiro.)

Continental Portuguese Examples

Note: In Portugal, "postais" is the natural way to refer to postcards.

1. Eu comprei vários postais para a minha mãe. (I bought several postcards for my mother.)
2. Ela adora colecionar postais de viagens. (She loves collecting postcards from trips.)
3. Escrevi alguns postais durante as férias. (I wrote some postcards during the holidays.)
4. Onde posso comprar postais desta cidade? (Where can I buy postcards of this city?)
5. Enviei postais a todos os meus amigos. (I sent postcards to all my friends.)