October 2023 - dovecot

Recommended changes for delivery from Exim
by jgh＠exim.org 05 Feb '24

05 Feb '24

Hi, Security changes to Exim have invalidated certain suggested configurations in the Dovecot wiki. As I do not have a Dovecot installation to test, I am not going to write any updates there. It would be good if someone would test these suggestions and then make updates as needed. 1) The use of $local_part and $domain in commands run by the "pipe" transport will be disallowed in the upcoming Exim release. These are currently noted as optional, with the "-m" flag to dovecot-lda. They should be replaced with validated (untainted) versions, commonly $local_part_data and $domain_data, developed via one of the several de-taint methods documented for Exim. The same applies to $original_local_part and $original_domain. 2) The use of $sender_address will likewise be disallowed. This and the "-f" flag can be dropped from the dovecot-lda command line, and the specification of a null "message_prefix" option removed. The defaults for a pipe transport will then prefix the message with a suitable Mbox "From " header line, which dovecot-lda is documented to extract the sender from. Both of these suggestions are back-compatible to the current 4.95 release of Exim, and will be required with the 4.96 release. -- Cheers, Jeremy Refs: - https://wiki.dovecot.org/LDA/Exim - https://doc.dovecot.org/configuration_manual/protocols/lda/

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JMAP support?
by Mark Constable 31 Jan '24

31 Jan '24

On Fri Jan 25 2019 Aki wrote: > There is no JMAP support in any dovecot version yet. Two years on so what is the status of JMAP support in Dovecot now?

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Replication going away?
by Vladimir Mishonov 26 Jan '24

26 Jan '24

Hello everyone. Just saw this commit in the official Github repo: https://github.com/dovecot/core/commit/4c04e4c30fd4817a8b0e11d04d9681173f69… Looking at the commit details, it appears that it completely removes the replication feature. I'm a bit perplexed by this change and am not sure what might be the justification for it. Personally, I find replication to be very useful, as it allows me to maintain a synchronized mirror of all of my mailboxes on my home server, for use as backup in case the primary server goes down for some reason. Perhaps there's some sort of replacement being planned for this feature? Or maybe the relevant code is simply going to be refactored to a plugin or external program, and there's nothing to worry about at all? In any case, I'd greatly appreciate if one of the developers could comment on this change. -- Kind regards, a concerned user of Dovecot (Vladimir)

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Forcing imap authentication failure for certain IP addresses
by Hippo Man 20 Jan '24

20 Jan '24

I'm running dovecot 2.3.18 under Debian 11. I want to do something that's a bit unusual: when IMAP connections are attempted from a few specific IP addresses, I want to force an IMAP authentication failure from those connections, no matter what user ID and password are specified. I know that I can use iptables to completely block imap access from those IP addresses to the IMAP ports. However, in these specific cases, I'd prefer that the connection goes through to dovecot, but for dovecot then to always generate authentication failures for those specific connections ... even if a valid user ID and password happen to be specified. Is there a way to do this in dovecot? Thank you very much in advance. -- hippoman(a)gmail.com Take a hippopotamus to lunch today. .---------, 0__0 / ( oo'---, / oo\ ,\ | | \ ,=__/ \ / / /------| /| |__|-' |__|'

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replicator: Panic: data stack: Out of memory when allocating 268435496 bytes
by Gerben Wierda 06 Dec '23

06 Dec '23

One step further in my quest to create a replacement mail server. I now have my old mail server (2.3.19.1, macOS + MacPorts) and my new (2.3.20, Alpine Linux, Docker, apk package). When I turn on replication it works, but, after a while I see: Jan 06 00:50:31 replicator: Panic: data stack: Out of memory when allocating 268435496 bytes Jan 06 00:50:32 replicator: Fatal: master: service(replicator): child 133 killed with signal 6 (core dumped) Jan 06 00:50:32 lmtp(pid 195 user sysbh): Warning: replication(sysbh): Sync failure: Jan 06 00:50:32 lmtp(pid 195 user sysbh): Warning: replication(sysbh): Remote sent invalid input: - I've removed synchronous operation for now (found a message on the net suggesting that) but is this known and what does it mean? Gerben Wierda (LinkedIn <https://www.linkedin.com/in/gerbenwierda>) R&A IT Strategy <https://ea.rna.nl/> (main site) Book: Chess and the Art of Enterprise Architecture <https://ea.rna.nl/the-book/> Book: Mastering ArchiMate <https://ea.rna.nl/the-book-edition-iii/>

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Can Dovecot Use Wildcard TLS Certificates?
by duluxoz 07 Nov '23

07 Nov '23

Hi All, Quick Q: Can dovecot use wildcard TLS Certificates? I'm having issues with a new dovecot/postfix stack set-up and I can't get mutt on the local box to connect via imap - its coming back with an SSL error, and as I'm using a wildcard cert for the domain I was wondering if that was my issue. If dovecot can use wildcard certs then I'll look elsewhere in my troubleshooting. Thanks in advance Cheers Dulux-Oz

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Setting up a new server
by James Cloos 30 Oct '23

30 Oct '23

I'm in the process of switching to dovecot for my lan imap and have a couple of questions. I want to keep the folder names unchanged. For mailing lists I use the posting address (eg foo(a)bar.co) for others I use / as the separator. If I use mdbox, will those choices cause any issues? My impression is not, but I'd like to be sure. Also I'd like to use imap-specific passwds for each user. My tests so far have used the login passwds for each user. Not necessarily virtual users, just imap-specific passwds. There is already a pgsql server handy; I take it that would be the way to go for passdb and userdb lookups, yes? Thanks, -JimC -- James Cloos <cloos(a)jhcloos.com> OpenPGP: 0x997A9F17ED7DAEA6

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Two-way TLS and other security for LMTP over the internet?
by forum＠ageofdream.com 29 Oct '23

29 Oct '23

Dovecot version 2.3.19.1 (9b53102964) Postfix version 3.5.18 We have a Postfix server that runs on a VPS with a hosting company and a Dovecot IMAP server that runs at the office. We want Postfix to push the mail it receives to the Dovecot IMAP server, using the least amount of intermediate software. This transfer occurs over the open internet. LMTP over TCP seems like a great solution, *if* it can be secured. But I'm not finding documentation on how to actually setup something like two-way TLS over LMTP. 1. Is there any setting in Dovecot where I can set a remote IP address (or hostname) that will be the only address that Dovecot's LMTP accepts connections from? 2. My current configuration options for LMTP in Dovecot look like: protocol lmtp { ssl_cert = </etc/ssl/imap/imap.crt ssl_key = </etc/ssl/imap/imap.key ssl_ca = </etc/ssl/imap/authority.crt ssl_verify_client_cert = yes auth_ssl_require_client_cert = yes } service lmtp { user = vmail inet_listener lmtp { address = * :: port = 24 } } With these settings, I can telnet from the Postfix server to the Dovecot server with LMTP, and I'm not convinced there is any encryption actually enabled or any TLS verification going on. Is there any reasonable security that can be setup to make this safe (within Dovecot and Postfix settings, not using VPNs and SSH tunnels)? If so, how?

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{ldap:objectGUID} returns binary data when used for user_attrs
by Andreas Haerter 26 Oct '23

26 Oct '23

Hi, there is an environment in which I have to use MS Active Directory for authentication and mail server user database, and I've run into a problem. I. The problem I want to retrieve the objectGUID attribute for the homedir path of the users. This attribute does never change, even when the username does or the account gets moved to another AD domain. However, the objectGUID is returned as binary gibberish when using the following setting: > user_attrs = \ > =home=/var/vmail/example.com/%LT{ldap:objectGUID}, \ It results in > # doveadm user uTesting > field value > user utesting > home /var/vmail/example.com/d ��n�aa_ o�� > mail maildir:~/mail Can someone reproduce this or offer a workaround? The only idea I had was hashing the value using =%M{ldap:objectGUID}. However, this approach would become problematic if the behavior changes and a proper string representation is returned, as expected, instead of the binary data. Therefore, I'm hesitant to use this method for now. A better approach would be encoding it as Base64, but I was unsuccessful to identify a fitting modifier at <https://doc.dovecot.org/configuration_manual/config_file/config_variables/#…>. Any ideas? II. Additional info Using other attributes for LDAP/Active Directory works as expected. E.g. > =home=/var/vmail/example.com/%LT{ldap:sAMAccountName} results in > # doveadm user uTesting > field value > user utesting > home /var/vmail/example.com/utesting > mail maildir:~/mail The objectGUID is indeed binary data, but IHMO, it should be handled differently when returned. E.g. there is a defined string representation, [MS-DTYP] section 2.3.4.3: <https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-dtyp/222af…> which links to: > curly braced GUID string: The string representation of a 128-bit > globally unique identifier (GUID) using the form > {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}, where X denotes a hexadecimal > digit. The string representation between the enclosing braces is the > standard representation of a GUID as described in [RFC4122] section 3. > Unlike a GUIDString, a curly braced GUID string includes enclosing braces. Some libs simply decide to return the data Base64 encoded (which would be OK, too). E.g. openldap-clients / ldapsearch does so with objectGUID and objectSid: > $ ldapsearch [...] > [...] > # uTesting, common, user, managed, example.com > dn: CN=uTesting,OU=common,OU=user,OU=managed,DC=example,DC=com > [...] > name: uTesting > objectGUID:: RCDirQPvGU6KQUFfIE/i2Q== > [...] > objectSid:: AQUAAAAAAAUVAAAALenCqsullBUfFoubWQQAAA== > [...] > sAMAccountName: uTesting > [...] Other software had comparable bugs or behavior , e.g. sssd ("Properly handle AD's binary objectGUID"): <https://bugzilla.redhat.com/show_bug.cgi?id=1205382> <https://github.com/SSSD/sssd/issues/3629> owncloud ("ensure that objectguid or guid really return binary data before converting it"): <https://github.com/owncloud/core/issues/8317> III. Software versions, config I can reproduce the issue on Fedora Server 38 > # cat /etc/redhat-release > Fedora release 38 (Thirty Eight) > # uname -r > 6.4.15-200.fc38.x86_64 > # dovecot --version > 2.3.20 (80a5ac675d) and CentOS 9 Stream: > # cat /etc/redhat-release > CentOS Stream release 9 > # uname -r > 5.14.0-364.el9.x86_64 > # dovecot --version > 2.3.16 (7e2e900c1a) I did not try a Debian-based distro yet. The config itself works fine, relevant settings just for reference (as there are not many examples on the internet, maybe useful for somebody): > auth_username_format = %Lu > > passdb { > driver = ldap > args = /etc/dovecot/dovecot-ldap.conf.ext > } > userdb { > driver = ldap > args = /etc/dovecot/dovecot-ldap-userdb.conf.ext > } with the following options to exclude inactive accounts, search smtp proxy addresses and having a mandatory group membership in SERVICE_EmailUsers: > base = OU=common,OU=user,OU=managed,DC=example,DC=com > scope = subtree > > user_filter = \ > (& \ > (objectClass=user) \ > (objectCategory=Person) \ > (|(sAMAccountName=%{username})(mail=%{username})(proxyAddresses=smtp:%{username}@%{domain})) \ > (!(userAccountControl:1.2.840.113556.1.4.803:=2)) \ > (memberOf:1.2.840.113556.1.4.1941:=SERVICE_EmailUsers) \ > ) > pass_filter = \ > (& \ > (objectClass=user) \ > (objectCategory=Person) \ > (|(sAMAccountName=%{username})(mail=%{username})(proxyAddresses=smtp:%{username}@%{domain})) \ > (!(userAccountControl:1.2.840.113556.1.4.803:=2)) \ > (memberOf:1.2.840.113556.1.4.1941:=SERVICE_EmailUsers) \ > ) I will blog about the config in more detail at https://foundata.com/en/blog/ soon, especially when the objectGUID is solved (maybe hashing it really the way to go). :-) Regards, Andreas -- foundata GmbH Steinhäuserstr. 20 76135 Karlsruhe Sitz der Gesellschaft: Karlsruhe Registergericht: Amtsgericht Mannheim, HRB 714807 Geschäftsführer: Andreas Haerter USt-IdNr.: DE284122682

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Correct sizing of CPU and RAM
by DeJa Wu 26 Oct '23

26 Oct '23

How to correctly calculate the number of CPUs and memory required for 1000 client mailboxes and beyond? Given that 30-50% of users will be constantly connected via IMAP. I looked for information and did not find any sizing in the documentation anywhere. Is there a way to calculate my required resources? BR, DeJa How to correctly calculate the number of CPUs and memory required for 1000 client mailboxes and beyond? Given that 30-50% of users will be constantly connected via IMAP. I looked for information and did not find any sizing in the documentation anywhere. Is there a way to calculate my required resources? BR, DeJa

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