Mail Submission Protocol

Tony Finch dot at
Thu Apr 22 06:07:49 CDT 2010

On 22 Apr 2010, at 00:07, Franck Martin <franck at> wrote:

> Consider also smtps port which should be treated like smtp port and  
> not like submission port, or simply do not listen on smtps as TLS is  
> available on smtp port via esmtp.

Er, no. TLS-on-connect aka smtps (as opposed to STARTTLS) is only used  
to support Microsoft MUAs that are more than a couple of years old.  
They only supported STARTTLS on port 25 and insisted on using the  
deprecated TLS-on-connect mode on all other ports. This meant they  
could not support standard Message Submission on port 587. Therefore  
you should treat smtps (TLS-on-connect on port 465) as the special  
Microsoft version of RFC 4409 message submission. That is, treat the  
protocols exactly the same wrt authentication, authorization,  
firewalls, address validation, etc.

f.anthony.n.finch  <dot at>

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