Hi,
basti <mailinglist@???> (Do 23 Jan 2014 15:46:09 CET):
> I'm more confused then ever.
>
> On the IMAP side of my Mailsystem is use
>
> PORT 993
> SSL/TLS with Encrypted password
>
> user@machine:~$ openssl s_client -connect myserver.de:993 -showcerts
> CONNECTED(00000003)
>
> **** SSl stuff ****
>
> ---
> * OK [CAPABILITY IMAP4rev1 CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT
> THREAD=REFERENCES SORT AUTH=CRAM-MD5 AUTH=CRAM-SHA1 IDLE ACL ACL2=UNION]
> Courier-IMAP ready. Copyright 1998-2011 Double Precision, Inc. See
> COPYING for distribution information.
> ^C
>
> I want to use the same on SMTP/Exim side of my Mailsystem.
> Which technique do you prefer for:
>
> port 25/465 or 587
> SSL/TLS with Encrypted password
25/smtp is for MTA -> MTA communication
TLS depends on the options offered by the receiving
and the options choosen by the sending side, thus
is part of the SMTP protocol (command STARTTLS)
465/smtps is used by some excotic (?) MUAs for message submission
TLS is negotiated on prior to the start of the
SMTP protocol
587/submission
is for MUA -> MTA communication
TLS depends on the options offered by the receiving
and the options choosen by the sending side, thus
is part of the SMTP protocol (command STARTTLS)
For SMTP TLS is a nice to have, I'd say.
For message submission I'd say you've no option, I'd always enforce the
use of STARTTLS befor authentication.
What you see on port 993 is "tls-on-connect", that is: TCP | TLS | IMAP
For SMTP you want to use port 465 for that. (Better: you do not want
this tls-on-connect at all! It's not standard.)
For SMTP it's up to you to drop the connection if you see 'rcpt to'
without having TLS established first. The same holds for submission,
where I would not offer AUTH without having TLS set up.
The '${if def:tls_cipher}' is a useful expansion:
begin acl
acl_check_rcpt:
…
accept domains = +local_domains : +relay_to_domains
local_parts = postmaster : abuse
require message = we accept tls connections only
condition = ${if def:tls_cipher}
begin auth
…
server_advertise_condition = ${if def:tls_cipher}
Best regards from Dresden/Germany
Viele Grüße aus Dresden
Heiko Schlittermann
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