Very slow mail download/notification with dovecot 2.3.7 and Thunderbird

27 Dec 2020


      Hi!
I know that there are many results if I search for "dovecot thunderbird
very slow" on Google but none of them helped me with my problem. :(  (I
already posted this on February 2020, but forgot to answer. O.o)
I am running Ubuntu 20.04 (4GB RAM, 40GB HDD with EXT4) server with the
following software:

Dovecot 2.3.7.2
---- All accounts are using Maildir
---- Sieve filters

Postfix 3.4.13
---- with opendkim, spamassassin, razor, pyzor, ....


And as IMAP client I am using Thunderbird 78.6 on Windows 10.
Sieve is used to sort some incoming mails into my 228 folders (56 INBOX.
folders and its subfolders (output of "find .INBOX.* -maxdepth 4 -type d
-print |wc -l")).  The total size of my Maildir directory is 5.5GB.
My problem is that it always takes very very long to synchronize the
INBOX and its subfolders. Even if there are only a few new messages to
be downloaded. Sometimes Thunderbird outputs something like "downloading
message 1 of 19" and it takes at least 60 seconds to download all of
them. None of these mails is larger than 5kB. And sometimes it seems
that the transfer is suspended for a long time and it takes >5 Minutes
to synchronize only a few mails. :(
And it seems that some folders are never updated in TB. In example I
sort all messages from this list into a "INBOX.Mailinglists.ML-Dovecot"
subfolder by using a simple sieve rule. But even after 10 minutes TB
thinks that there are no new messages. As soon as I click on the
ML-Dovecot folder I see in the /var/log/dovecot-info.log file that TB
logs on to the server and then displays hundreds, of new messages. I
checked twice but I have subscribed to all 228 folders.
How can I find the bottleneck?
Is there a test tool available that simulates a simple mail client and
can analyse an IMAP server?
This is the output of "dovecot -n":
===============================
# 2.3.7.2 (3c910f64b): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.7.2 ()
# OS: Linux 5.4.0-54-generic x86_64 Ubuntu 20.04.1 LTS
# Hostname: mail.XXXXXXX.de
auth_mechanisms = plain login
debug_log_path = /var/log/dovecot-debug.log
default_client_limit = 15653
default_process_limit = 5200
first_valid_uid = 150
info_log_path = /var/log/dovecot-info.log
last_valid_uid = 150
lda_original_recipient_header = X-Original-To
log_path = /var/log/dovecot-error.log
login_log_format_elements = user=<%u> method=%m rip=%r lip=%l mpid=%e %c %k
mail_gid = mail
mail_home = /var/vmail/%d/%n
mail_location = maildir:~/Maildir
mail_uid = vmail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope
encoded-character vacation subaddress comparator-i;ascii-numeric
relational regex imap4flags copy include variables body enotify
environment mailbox date index ihave duplicate mime foreverypart extracttext
namespace inbox {
inbox = yes
location =
mailbox Archive {
special_use = \Archive
}
mailbox Drafts {
special_use = \Drafts
}
mailbox Junk {
special_use = \Junk
}
mailbox Sent {
special_use = \Sent
}
mailbox "Sent Messages" {
special_use = \Sent
}
mailbox Trash {
special_use = \Trash
}
prefix =
}
passdb {
args = /etc/dovecot/dovecot-sql.conf.ext
driver = sql
}
plugin {
sieve = ~/.dovecot.sieve
sieve_default = /var/vmail/global.sieve
sieve_dir = ~/sieve
}
postmaster_address = thorsten@MY_DOMAIN.TLD
protocols = " imap sieve pop3"
service auth {
unix_listener /var/spool/postfix/private/auth {
group = postfix
mode = 0666
user = postfix
}
unix_listener auth-userdb {
group = mail
mode = 0666
user = vmail
}
}
service imap-login {
inet_listener imap {
port = 143
}
inet_listener imaps {
port = 993
ssl = yes
}
process_limit = 50
process_min_avail = 2
service_count = 20
}
service imap {
process_limit = 1024
}
service managesieve-login {
inet_listener sieve {
port = 4190
}
service_count = 0
}
ssl_cert =  was automatically rejected:%n%r
}
protocol imap {
imap_client_workarounds = tb-extra-mailbox-sep
imap_idle_notify_interval = 10 mins
mail_max_userip_connections = 100
mail_plugins =
}
protocol sieve {
info_log_path = /var/log/dovecot-sieve.log
mail_max_userip_connections = 100
managesieve_implementation_string = Dovecot Pigeonhole
managesieve_max_line_length = 65536
Output of "free -h":
free -h
total        used        free      shared  buff/cache  
available
Mem:          3.8Gi       1.7Gi       1.1Gi        10Mi      
958Mi       1.7Gi
Swap:         1.0Gi       375Mi       648Mi
Thank you very much!
Thorsten

Very slow mail download/notification with dovecot 2.3.7 and Thunderbird​

ml_dovecot＠thorsten-reichelt.de

Output of "free -h":

free -h total used free shared buff/cache available Mem: 3.8Gi 1.7Gi 1.1Gi 10Mi 958Mi 1.7Gi Swap: 1.0Gi 375Mi 648Mi

Very slow mail download/notification with dovecot 2.3.7 and Thunderbird