I believe that it’s more used in dialects spoken in Brazil than elsewhere, but even in Brazil it’s considered poor grammar. Specially given that both nós conjugations¹ and the synthetic future² are falling into disuse, so it sounds like trying to speak fancy and failing hard at it.

EDIT: now it clicked me why you likely said so; it’s common in European dialects to use “a enviar” (gerundive infinitive) instead of “enviando” (traditional gerund)³. The phenomenon that I’m talking about can be used with either, e.g. “estaremos a enviar”; for me it’s the same issue, people would say “estaremos a enviar” instead of “enviaremos” to throw the event into a distant future that might never happen.

1. They’re still fairly used by older people in speech, but there’s a clear gen gap with younger folks using “a gente” almost exclusively.
2. almost completely replaced by conjugated ir + infinitive.
3. Note that “enviando” is still fairly used in Alentejo and the Algarve.