[Dovecot] Size of Mailbox affecting the sending of mail?

[Stan Hoeppner]

On 8/24/2012 5:53 AM, Tim Smith wrote:

Hay Tim,

> Having set up my mail server (Dovecot/Postfix), users are experiencing
> long delays (a couple of minutes) when sending mail from mail client
> such as Thunderbird - this increases with attachments. Having had a
> brief discussion with someone, they mentioned that the reason that this
> may be to do with the size of the mailbox. I couldn't see the rationale
> behind this unless Dovecot is syncing the mailbox after every sent mail
> (due to possibly saving the sent item?) The mail is being delivered
> successfully but the amount of time it is taking to complete the action
> is far too long!

You probably have multiple factors involved in this mail sending delay
issue.

One may be that you're not bypassing your Postfix restrictions on your
submission service.  To fix this, disable your restrictions in the
master.cf service definition of your submission service.  For example:

587      inet  n       -       n       -       -       smtpd
        -o smtpd_enforce_tls=yes
	-o smtpd_sasl_auth_enable=yes
        -o content_filter=
        -o smtpd_client_restrictions=
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,\
	   permit_sasl_authenticated,reject
        -o receive_override_options=no_unknown_recipient_checks,\
	   no_address_mappings,no_header_body_checks

This should squash any/all delays in Postfix submission.

Another is the fact you're storing the users' Sent folders on the IMAP
server.  Typically there's nothing wrong with this.  I do this and I see
zero delay in Tbird.  If a good portion of the delay you're seeing is
Tbird copying messages to the Sent folder then I'd say you may have a
duplex mismatch or some other network layer issue.

What is the network topology between these client MUAs and the server?
Full duplex fast ethernet?  GbE?  Or is the server at a remote location,
say a colo/VPS server, and your clients are submitting over a shared
ADSL/cable circuit to the server?  If this is the case you'll always
have substantial delays as the real outbound transmission rate of the
best ADSL/cable circuits is only 500-1000 Kbps.  Sending an attachment
over such a pipe is always going to be slow, doubly so if you're copying
to an IMAP Sent folder over the same connection, plus sharing it for web
browsing, etc, amongst many users.

If this is a SOHO environment with shared ADSL/cable the server needs to
be on site, with clients connected via ethernet.  This will allow
instantaneous submission and Sent copying, while pushing the delay to
the Postfix outbound queue, where it's invisible to your users.

-- 
Stan