@semnosao tenta bater no servidor de destino via telnet (`telnet mailsec.protonmail.ch 22`). se não conectar, é isso mesmo :/
tenta tbém o gmail-smtp-in.l.google.com, pra ter certeza que não é o protonmail sendo diferentão
自前で建ててるmail server (CentOS7 sendmail)からGoogle gmail にメールが転送できない。地元のメールアドレスには転送できてるけど。どうも、mail serverは IPv6を使っているけどそれが逆引きできない、というような話らしい。自分のPleromaが壊れる前からの問題。sendmailがIPv6を使って送信しなければよいのではないかと思うけどまだできない。うーん。
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Subject: Returned mail: see transcript for details
(reason: 550-5.7.1 [ここに私のmail serverのIPv6アドレス] The IP you're using to send mail is not)
(expanded from: )
----- Transcript of session follows -----
... while talking to gmail-smtp-in.l.google.com.:DATA
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