Expuning & Purging doesn't fully remove emails?

[Zelic Bojan]

I'm using haproxy because of convenience and familiarity, the setup also seemed easier then director.

The manual does state to use a stick-table with dovecot IMAP.... my issue is with Postfix & Dovecot LMTP though(along with replication)

Using stick-tables (based on source IP) in the same way wouldn't solve the issue. Since different IPs can send emails to the same mailbox and because replication occurs simultaneously on different servers you might still run into the problem.

the haproxy postfix backend would need to be setup in an active/passive way... or using stick-tables to ensure only 1 server is active at a time.

The following configuration balances the servers so they switch off every minute that passes without a connection coming through. Ensuring only one server is receiving mail.

backend smtp_10025
  balance roundrobin
  option tcp-check
  server mail01 10.0.0.100:10025  check check-send-proxy send-proxy
  server mail02 10.0.0.101:10025  check check-send-proxy send-proxy
  stick on int(1)
  stick-table type integer size 1 nopurge expire 60s
  tcp-check expect rstring ^220
  tcp-check send QUIT\r\n
  timeout server 600s

The purging issue was a result of a round-robin'd connection to postfix where every connection alternated the server that email was coming through. Postfix stored the mail locally to dovecot and dovecot replicated it across instances. In theory this should've worked, (and for multiple months it did!)
________________________________
From: Marc Roos <M.Roos at f1-outsourcing.eu>
Sent: Wednesday, August 26, 2020 11:58 PM
To: Zelic Bojan <bojan.zelic at kudelskisecurity.com>; dovecot <dovecot at dovecot.org>
Subject: RE: Expuning & Purging doesn't fully remove emails?


But is that not adviced in the manual[1]? I am also in the process of
setting up dovecot behind a haproxy. Still testing with this. I was
wondering why one would choose haproxy and not eg dovecot proxy (with
director)



[1]
https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwiki2.dovecot.org%2FHAProxy&data=02%7C01%7Cbojan.zelic%40kudelskisecurity.com%7Ca3c2c2eaabe444ef253008d84a5693ff%7Ce573309544254f08b6ba487b9a46a425%7C0%7C1%7C637341083000478508&sdata=zKRtkWbI6VzCpUJmdLudYA9M9noilPr%2Bsx48DY1x1mE%3D&reserved=0



-----Original Message-----
From: Zelic Bojan [mailto:bojan.zelic at kudelskisecurity.com]
Sent: woensdag 26 augustus 2020 23:39
To: dovecot at dovecot.org
Subject: Re: Expuning & Purging doesn't fully remove emails?

​I managed to figure this out.


Just wanted to follow up if anyone in the future encounters the same
issue.

I am using HAProxy along with dovecot replication. When an email comes
in... it is round robin'd to each of the 2 dovecot/postfix servers. I
have postfix running on each server and it uses the local dovecot LMTP
service for storing the mails.

We sometimes get surges of emails(hundreds or thousands in a couple of
seconds). Each alternative request hits a different mail server and then
should be replicated. The replication works and we don't encounter
missing or duplicated emails.

However, when I purge expunged emails, somehow this does not fully
remove them when it's setup in this fashion.

I ran 2 tests:
1) I send 1000 emails to the loadbalancer(round-robin), expunge on both
servers & purge them on both servers, recreate the indexes... ~200
emails come back.
2) I send 1000 emails to one of the mail servers, expunge & purge them,
recreate the indexes... 0 emails come back.

My fix is to remove the round robin load balancing and use sticky tables
in HAproxy.



________________________________

From: Zelic Bojan
Sent: Thursday, August 20, 2020 1:42 PM
To: dovecot at dovecot.org <dovecot at dovecot.org>
Subject: Expuning & Purging doesn't fully remove emails?

Hello, I'm facing an issue where deleted emails keep re-appearing after
my mailbox index gets recreated.  I'm running version 2.2.36 of dovecot,
but I tested the same scenario under 2.3.10. I'm also using mdbox,
autoexpunge, and using dovecot replication.

I've had several instances now where some expunged emails show up again
in a mailbox. I noticed this error:

  doveadm: Error: Corrupted dbox file
/var/mail/virtual/mailbox at domain.com/mdbox/storage/m.3228 (around
offset=1988744): msg header has bad magic value

which caused the index to get rebuilt... however several times now, the
indexes got rebuilt even though there doesnt seem like there was any
error... so im not sure why that is.

  lmtp(13910): Warning: fscking index file
/var/mail/virtual/mailbox at domain/mdbox/storage/dovecot.map.index
  lmtp(13910): Warning: fscking index file
/var/mail/virtual/mailbox at domain/mdbox/storage/dovecot.map.index
  lmtp(13910): Warning: mdbox
/var/mail/virtual/mailbox at domain/mdbox/storage: rebuilding indexes

I'm not sure why these mails keep coming back though... or if there's
anything that I can do to limit the number of emails that get restored.

I want to make sure expunged & purged emails stay expunged & purged. If
I run a purge and then force index recreation... why would expunged
emails come back? Shouldn't I expect them all to be deleted & purged?
Does expunge not expunge all emails? (In production, I'm running
autoexpunge but this test below shows what happens when I attempt to
expunge everything)

  doveadm search -u email at domain all | wc -l
  # output 22096

  doveadm expunge -u email at domain mailbox '*' all
  doveadm search -u email at domain all | wc -l
  # output: 0

  doveadm purge -u email at domain
  doveadm dump /var/mail/virtual/email at domain/mdbox/storage/ | grep -c
'ref.*\b0\b'
  # output: 0

  doveadm force-resync -u email at domain Inbox
  # output:
  # doveadm(email at domain): Warning: fscking index file
/var/mail/virtual/email at domain/mdbox/storage/dovecot.map.index
  # doveadm(email at domain): Warning: mdbox
/var/mail/virtual/email at domain/mdbox/storage: rebuilding indexes
  # doveadm(email at domain): Warning: fscking index file
/var/mail/virtual/email at domain/mdbox/storage/dovecot.map.index

  doveadm search -u email at domain all | wc -l
  # output: 843

I would expect the output to be 0. Theoretically I deleted all emails
and purged all emails. Nothing should be left on the disk? However... I
can see there are still m.* files in mdbox/storage for the mailbox.

Overall, I'm not sure why the index got recreated... but I'm trying to
limit the impact of mailbox corruption so that deleted emails do not
come back if the index is somehow recreated again.

If I were to re-run expunge, purge, and force-resync a 2nd time... it
does get emptied out, but I'm not looking to run force-resync
intentially since it causes dataloss with mdbox, and re-running only
expunge & purge doesn't seem to do anything.

Bojan Zelic
Sr. IT Infrastructure Engineer


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