The only concern is the bandwidth since it has been almost fully utilized. (not all the time)

This is what i referred
http://www.postfix.org/rate.html

That is why i changed those values.

Thanks,

Connection timed out

Are you sure no issues with you network?
local network and mail server.

And it's not suggest to change local_destination_concurrency_limit, default_destination_concurrency_limit.

But now this is getting worst. Receiving having no problems at the moment. The mail queue is getting higher and higher.
The maillog is full of with timeouts.

Sep 10 11:25:11 mail postfix/qmgr[14968]: EAC106C88DF: skipped, still being delivered
Sep 10 11:25:11 mail postfix/qmgr[14968]: 68AA96C895C: skipped, still being delivered
Sep 10 11:25:11 mail postfix/qmgr[14968]: 6270A6C88F7: skipped, still being delivered
Sep 10 11:25:11 mail postfix/qmgr[14968]: 443966C8935: skipped, still being delivered
Sep 10 11:25:11 mail postfix/qmgr[14968]: 6362B6C8948: skipped, still being delivered

Sep 10 11:26:27 mail postfix/smtp[16906]: 549D86C890F: to=<fzurfick@amana.lk>, relay=mailmx1.dialogbb.net[203.189.73.2]:25, delay=4369, delays=3418/0.03/343/608, dsn=4.4.2, status=deferred (conversation with mailmx1.dialogbb.net[203.189.73.2] timed out while sending message body)
Sep 10 11:26:29 mail postfix/smtp[19771]: connect to hnbmail.hnb.lk[203.115.31.154]:25: Connection timed out
Sep 10 11:26:52 mail postfix/smtp[15211]: 549D86C890F: to=<thilina.fernando@dialog.lk>, relay=spamwall.dialog.lk[202.69.200.143]:25, delay=4394, delays=3418/0.04/608/368, dsn=4.4.2, status=deferred (conversation with spamwall.dialog.lk[202.69.200.143] timed out while sending message body)
Sep 10 11:26:59 mail postfix/smtp[19771]: connect to ho.hnb.lk[203.115.31.154]:25: Connection timed out
Sep 10 11:26:59 mail postfix/smtp[19771]: 549D86C890F: to=<Udita.Jayaratne@hnb.lk>, relay=none, delay=4401, delays=3418/0.05/983/0, dsn=4.4.1, status=deferred (connect to ho.hnb.lk[203.115.31.154]:25: Connection timed out)
Sep 10 11:26:59 mail postfix/smtp[19771]: 549D86C890F: to=<aryaprema@hnb.lk>, relay=none, delay=4401, delays=3418/0.05/983/0, dsn=4.4.1, status=deferred (connect to ho.hnb.lk[203.115.31.154]:25: Connection timed out)

even small capacity emails also getting stuck in the queue. for eg: email with 3MB attachment stuck in the queue for more than a day. Most if the emails having same scenario.

I have set the bellow parameters in main.cf
     local_destination_concurrency_limit = 2
    default_destination_concurrency_limit = 50

Nothing happened still the same. Please help me..!!!

Sep 10 01:25:03 mail postfix/error[1517]: B74246C88E9: to=<user@gmail.com>, relay=none, delay=104, delays=0.01/104/0/0, dsn=4.4.2, status=deferred (delivery temporarily suspended: conversation with alt1.gmail-smtp-in.l.google.com[209.85.133.27] timed out while sending message body)

It looks like a network connection issue at that time.

Hi,

I have iRedmail 4.0 installed in a RHEL 5 system. My emails (sent) are getting delayed for many hours and the mail queue is increasing heavily. 
This is a sample output which i have sent from the server using "mail" command to google mail. The username of the gmail is a valid one and here I have replaced it.

Sample mailllog entry

Sep 10 01:23:19 mail postfix/pickup[1072]: B74246C88E9: uid=0 from=<root>
Sep 10 01:23:19 mail postfix/cleanup[1444]: B74246C88E9: message-id=<20090909195319.B74246C88E9@mail.xyz.lk>
Sep 10 01:23:19 mail postfix/qmgr[1073]: B74246C88E9: from=<root@mail.xyz.lk>, size=286, nrcpt=1 (queue active)
Sep 10 01:25:03 mail postfix/error[1517]: B74246C88E9: to=<user@gmail.com>, relay=none, delay=104, delays=0.01/104/0/0, dsn=4.4.2, status=deferred (delivery temporarily suspended: conversation with alt1.gmail-smtp-in.l.google.com[209.85.133.27] timed out while sending message body)

All were working fine and this was started with an error in log "mysqld.log", "Table './policyd/helo' is marked as crashed and should be repaired". Then i was able to repair the helo table with "repair table" and it was resolved. But still my emails are getting delayed.

Can you give me a hint on this?

Thanks,
Sandun

just a quick update.
The email was sent
Sep 10 01:33:14 mail postfix/qmgr[1073]: B74246C88E9: from=<root@mail.xyz.lk>, size=286, nrcpt=1 (queue active)
Sep 10 01:33:27 mail postfix/smtp[1647]: B74246C88E9: to=<user@gmail.com>, relay=gmail-smtp-in.l.google.com[209.85.222.22]:25, delay=608, delays=594/0.04/12/1.4, dsn=2.0.0, status=sent (250 2.0.0 OK 1252526687 30si4522097pzk.54)
Sep 10 01:33:27 mail postfix/qmgr[1073]: B74246C88E9: removed

this was a few KB email and it took almost 10 mins to deliver.

Thanks,
Sandun

I have iRedmail 4.0 installed in a RHEL 5 system. My emails (sent) are getting delayed for many hours and the mail queue is increasing heavily. 
This is a sample output which i have sent from the server using "mail" command to google mail. The username of the gmail is a valid one and here I have replaced it.

Sample mailllog entry

Sep 10 01:23:19 mail postfix/pickup[1072]: B74246C88E9: uid=0 from=<root>
Sep 10 01:23:19 mail postfix/cleanup[1444]: B74246C88E9: message-id=<20090909195319.B74246C88E9@mail.xyz.lk>
Sep 10 01:23:19 mail postfix/qmgr[1073]: B74246C88E9: from=<root@mail.xyz.lk>, size=286, nrcpt=1 (queue active)
Sep 10 01:25:03 mail postfix/error[1517]: B74246C88E9: to=<user@gmail.com>, relay=none, delay=104, delays=0.01/104/0/0, dsn=4.4.2, status=deferred (delivery temporarily suspended: conversation with alt1.gmail-smtp-in.l.google.com[209.85.133.27] timed out while sending message body)

All were working fine and this was started with an error in log "mysqld.log", "Table './policyd/helo' is marked as crashed and should be repaired". Then i was able to repair the helo table with "repair table" and it was resolved. But still my emails are getting delayed.

Can you give me a hint on this?

Thanks,
Sandun