Parece que a DO está desativando SMTP nos seus planos de hospedagem do Discourse

[supermathie (Michael Brown)]

O bloqueio da porta 25 de saída por padrão pela Digital Ocean está em vigor há anos. Isso não é novidade.

Matt explica bem aqui:

Proposed changes to discourse-setup because Digital Ocean blocks outbound smtp

OK then, let me give you the full spiel, then: Port 25 outbound is an obvious candidate for filtering, because if you can hit the Internet on port 25, you can deliver e-mail to practically anyone. If that e-mail is unwanted, the only useful “identity” information that the recipient has to try and prevent further abuse is the sending IP address. That identity is tied, in general, to a hosting provider, not an individual subscriber, so any reputation hit for spamming goes, in the first instanc…