> On Dec 26, 2017, at 8:29 PM, Tom Maier <[hidden email]> wrote:
> Within my uni project I have to implement additional SMTP commands in
> order to upload or download data (e.g., base64 encoded data). This is
> why my initial idea was to add functionality to the smtpd server of
> Postfix by defining a SMTP service extension. Thus it would be possible
> to provide the "upload" command only for previously authenticated users.
> As opposed to this the "download" command is available for everyone.
> What do you think about this concept?
Why SMTP and not HTTP or IMAP? What about this application makes it
a natural fir for an asynchronous store and forward protocol? Remember
that SMTP servers are message routing engines not mail store access
providers. Postfix does not read users' mailboxes, and often does
not even know where they are (e.g. with LMTP or pipe(8) handoff).
Postfix is NOT Microsoft Exchange, which combines message routing with
mailstore access, for that your closest approximation is Zimbra and the
the like. Many mailstores include HTTP interfaces, and these can be
used for various collaborative applications. Message routing is in
steady state stateless, while the MTA keeps track of a working queue
in which messages might persist for some days, nothing stays in the
queue long-term, and once a message is delivered, it is no longer
the MTA's problem.
Bottom line, it sounds rather unlikely that your problem demands an
ESMTP extension. Those just tweak message handling en-route to a
mailstore, but should not be confused with groupware support.