On Tue, Mar 17, 2015 at 2:15 PM, Marco Gaiarin <marcogaio@???> wrote: >
>
> Ah. Someone can explain me because other protocols, eg IMAP, have a
> compression extension, while SMTP no?
>
> It's not the protocol which has the extension, but the extension was
written for the protocol.
The distinction is important, because extensions like these are written
afterwards, usually in response to somewhat enthusiastic responses to
perceived needs.
Consider typical e-mail usage for end users:
IMAP is used for downloading all the mail you get from others, possibly on
multiple devices (PCs, tablets, phones). SMTP is used for sending all your
mail, only once per device.
Compression is also not very useful for sending or receiving attachments,
but mostly for metadata, textual content or HTML, and even on a pretty bad
connection, sending a normal message is rarely a challenge.
But with IMAP, you will typically synchronize metadata frequently, e.g.
every 5 or 15 minutes.
So, conceding the point that compression has a use in e-mail handling for
MUAs, it's mostly useful for IMAP, conceivably somewhat useful for POP with
"leave mail on server" madness, and hardly useful for SMTP.
For server to server connections, the overhead for compressing and
decompressing may be undesirable.
--
Jan
