Diagnostic: "Le port sortant 25 semble être bloqué."

[ljf]

[en] The SMTP mail server cannot send emails // [fr] Le serveur mail SMTP ne peut pas envoyer de courriels

So the issue was due to a problem on YunoHost infra (rebooted around 14:43). I have just found the issue and fixed it, the monitoring was crying but we think it was a false positive.