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That's interesting. I wonder whether an ISP could block traffic using TLS SMTP ports to force opportunistic senders to revert to plaintext. I suspect this may
by spacebanana7 3y ago
That's interesting. I wonder whether an ISP could block traffic using TLS SMTP ports to force opportunistic senders to revert to plaintext.
I suspect this may be possible because TLS SMTP uses port 587, rather than 443 like other TLS connections.
https://www.cloudflare.com/en-gb/learning/email-security/smtp-port-25-587/ https://www.cloudflare.com/en-gb/learning/email-security/smt...
- Repulsion9513 3y agoThe SMTP that we're talking about uses port 25, not port 587 (or 465). But yes, an ISP could block the STARTTLS negotiation. Port 587 is submission - an end-user's client talking to their email provider's SMTP server. Port 25 is smtp - your email provider's SMTP server talking to the recipient's email provider's SMTP server. Port 443 is https - not TLS. TLS can operate over any port you like. The port is determined by the service being used, not by the fact that it's TLS.