Detect SMTP blocking - Githubissues

ooni / probe

OONI Probe network measurement tool for detecting internet censorship

https://ooni.org/install

BSD 3-Clause "New" or "Revised" License

760 stars 142 forks source link

Open FedericoCeratto opened 4 years ago

FedericoCeratto commented 4 years ago

Cleartext SMTP on port 25 is often blocked due to concerns around spam. Encrypted SMTP on higher ports is usually not blocked.

hellais commented 3 years ago

We might also look into detecting SMTP with STARTTLS downgrade attacks as has been seen in the wild here: https://discourse.mailinabox.email/t/thunderbird-starttls-error/8135