16
votes
Postfix smtps and submission confusion
TL;DR
The new recommendation is to support both submissions/smtps and submission with STARTTLS for the time being, phasing out the later once it's not used anymore. (The same recommendations also ...
- 261
11
votes
Accepted
Send test mail using telnet via smtps (465) port
SMTP session to smtps(465) port using telnet
Connections to smtp (25) start as unencrypted.
Connections to smtps (465) start/negotiate encryption before any SMTP protocol level communication.
You ...
- 6,278
10
votes
Accepted
RFC for "Received: With ESMTPS"
How about RFC3848
Abstract
This registers seven new mail transmission types (ESMTPA, ESMTPS,
ESMTPSA, LMTP, LMTPA, LMTPS, LMTPSA) for use in the "with" clause of
a Received header in an ...
- 116k
4
votes
Accepted
How to set up DKIM using Let's Encrypt?
The answer to this question is: you’re not supposed to.
According to the RFC:
Signature applications require some level of assurance that the
verification public key is associated with the claimed ...
- 323
4
votes
Redirect OR warn (during initial negotiation) SMTP submitters to use TLS on port 587 - leave 25 explicitly blocked by firewall for better security
Is there a way to indicate that to a requesting client/scanner/MTS server that SMTP requires TLS on port 587
Assuming MTS is a typographic error and you meant MTA.
587 is not secure SMTP, 587 is ...
- 946
3
votes
Accepted
Postfix is not responding on port 465 (SMTPS)
I'll do my best to give you some ideas, things to try...
Perhaps referring to the port numerically rather than by service name will help
From http://www.postfix.org/master.5.html
Service name
...
- 6,330
2
votes
nmap vulnerability scan reports " smtps on port 465 ssl-dh-params" vulnerability, on Ubuntu 20.04 webserver. How to close the vulnerabilty?
Anonymous TLS is the kind of configuration is also known as "TLS without certificates". There is no chain of trust for server's keypair, therefore absolutely no protection from MitM attacks. ...
- 12.6k
1
vote
Self-signed certificate error with exim: CA is unknown
This is Exim showing that the client is complaining about a self-signed cert. More details here.
Specifically, "A TLS fatal alert has been received" is followed by the message that the client sent ...
- 1,202
1
vote
Send test mail using telnet via smtps (465) port
The other answers are correct. You can use either gnutls-cli or openssl s_client to do a STARTTLS on port 465.
I just want to point out that some servers may still refuse to talk to you if your line ...
- 8,000
1
vote
Send test mail using telnet via smtps (465) port
Since this Q&A came up again on the front page
The canonical tool (almost always already installed as well) is OpenSSL
The relevant sub command to test both explicit TLS / SSL as well as ...
- 80.3k
1
vote
How can i redirect smtp port 25 to port 465
You need to use a mail hop service if port 25 is blocked by your ISP. This could also be a third party spam filtering service that is able to deliver email to another port. The rest of the internet ...
- 2,884
1
vote
Accepted
Do any reputable mail servers require STARTTLS encryption for SMTP delivery?
No.
Generally they can't do this since still very large majority of mail addresses are handled by non-TLS capable servers.
However some large providers (and the first was Gmail I believe) started "...
- 304
Only top scored, non community-wiki answers of a minimum length are eligible