This has been a productivity hogger for us for quite a few weeks and we really had no clue at it first. What I noticed was after enabling logging on trac.ini:

[logging]
log_file = trac.log
log_level = CRITICAL
log_type = file

was that every post was being sent to an SMTP server.

2008-03-09 19:50:49,323 Trac[__init__] DEBUG: Dispatching <request>
2008-03-09 19:50:49,335 Trac[__init__] DEBUG: action controllers: [
<trac>]
2008-03-09 19:51:48,483 Trac[__init__] INFO: Sending SMTP notification to 192.168.1.15:25 to [u'rupert@cybersoftchina.com', u'dev@cybersoftchina.com']
2008-03-09 19:51:53,610 Trac[__init__] DEBUG: Retrieving session for ID 'rupert'
2008-03-09 19:51:53,654 Trac[__init__] DEBUG: Dispatching <request>
</request></trac></request>

The culprit as you expected was my slow qmail server which for some reason I can’t figure out for now.

Workaround
I have to disable email alerts for every new/update ticket for the time being.

[notification]
admit_domains =
always_notify_owner = true
always_notify_reporter = true
always_notify_updater = true
ignore_domains =
mime_encoding = base64
#smtp_always_bcc =
#smtp_always_cc = dev@cybersoftchina.com
#smtp_default_domain =
#smtp_enabled = true
#smtp_from = trac@cybersoftchina.com
#smtp_from_name = Trac Auto Notification CNCPHS
#smtp_password = cybertrac2007
#smtp_port = 25
#smtp_replyto = dev@cybersoftchina.com
#smtp_server = 192.168.1.15
#smtp_subject_prefix = __default__
#smtp_user = trac@cybersoftchina.com
ticket_subject_template = $prefix #$ticket.id: $summary
use_public_cc = false
use_short_addr = false
use_tls = false