Client issues


This page is copied from old wiki and may contain old information. If you do find client(s) that need special configuration, or no longer need it, please let us know.

It seems to be quite difficult to implement a working IMAP client. Best Practices for Implementing an IMAP Client tries to help you with it.

Negative UIDs

Invalid messageset: 1181461470:-1181461446.

IMAP uses unsigned 32bit integers for unique message identifiers. Unfortunately a lot of IMAP clients use 32bit signed integers, which means that if the UIDs go higher than 2147483647, they’ll wrap to negative integers. This causes errors such as above.

However normally the UIDs should never go that high, so it’s possible to avoid this problem.

Earlier Dovecot versions had bugs which could cause X-UID: headers in incoming messages to grow the UIDs too high. Some spam messages especially contained these intentionally broken X-UID: headers.

With newer Dovecot versions these broken X-UID: headers aren’t practically ever used. It happens only if the mail has a valid X-IMAPbase: header, X-UID: header and the mail is written to an empty mbox file. Note that this can happen only new mboxes, because expunging all messages in a mailbox causes Dovecot to create a metadata message at the beginning of the mbox file.

In any case it’s still a good idea to filter out X-UID: and other metadata headers in your MDA. Dovecot’s deliver does this internally. See mbox problems for a list of headers to filter out.


Fixing is done by letting Dovecot update UIDVALIDITY value and recreate the UIDs beginning from one. This means that client’s local cache will be invalidated and the client will be required to download all the messages again.


Delete Dovecot’s index files (eg. .imap/INBOX/) and X-IMAP: and X-IMAPbase: headers from the mbox file.


This should really never be a problem with Maildir. If however you have managed to cause it somehow (by receiving 2 billion mails?), you can recreate the UIDs by deleting dovecot-uidlist file.

Some known clients

Appsuite webmail

Works fine.


On Mac OS X Leopard 10.5 appears to support subscribe/unsubscribe by right clicking on a mailbox, selecting ‘Get Account Info’ and selecting ‘Subscription List’ from tabs. This however doesn’t really work with any IMAP server.

Apple Mail 3.6 (that comes with OS X 10.5 Leopard) supports subscribing/unsubscribing to folders in the public namespace.


  • You should enable pop3_client_workarounds = outlook-no-nuls workaround with POP3.

  • If some Outlook users don’t see new or sent mails in the appropriate folders after a migration from UW IMAPd even if they are visible in other clients (e.g. Roundcube, Thunderbird, or on the disk itself), and you get the error message “BAD Error in IMAP command UID: Invalid UID messageset” in the log or rawlog: It helps to remove the problematic IMAP account completely from Outlook and recreating it again there. It speaks a different IMAP afterwards, so there are reasons to believe it caches the details of some server on the first connect and doesn’t refresh them even if you change the server’s hostname in the account settings.

Outlook Express 6

Netscape Mail

I’m not actually sure what version exactly this refers to.


  • Some versions don’t support creating subfolders with mbox format. Evolution in Ubuntu Gutsy, 2.12.0-0ubuntu5, does support creating subfolders, at least when the parent folder is empty.


Seems to be OK.


Everything works perfectly with Dovecot.


  • If you’re using mbox, dbox or Maildir with :LAYOUT=fs ,

  • If you’re using mbox

    • If you are not using a technique to allow folders that contain both sub-folders and messages (e.g. see Mbox Child Folders Configuration) then you will have to disable “Server supports folders that contain sub-folders and messages” setting from Thunderbird. Enhancement request.

  • Versions of Thunderbird from at least 17 (possibly earlier) up to 24.0 display incorrect new mail counts in the New Mail notification box. This is due to a bug in Thunderbird’s handling of the CONDSTORE extension. See Bug Report for details and a client-side workaround.


  • New mutt versions supporting IDLE command will hang with Dovecot versions earlier than v1.0beta3. Upgrade Dovecot or disable IDLE by setting imap_idle=no in .muttrc.

  • Using mutt with IMAP


Seems to be OK.


  • Configuration asks IMAP server name for some workarounds. There has been a Dovecot option since 1.4.6 and 1.5.1. For older SquirrelMail versions, select the “other” option and remove the default INBOX-prefix.

Horde IMP

Dovecot namespace detection works automatically with any recent version of IMP (4.1+).

Quota support is now integrated into the ‘imap’ driver (as of horde-groupware V1.2), an example config of /imp/config/servers.php is:

$servers['imap'] = array(
    'name' => 'IMAP Server',
    'server' => 'localhost',
    'hordeauth' => false,
    'protocol' => 'imap/notls',
    'port' => 143,
    'quota' => array('driver'=>'imap'),

RoundCube Webmail

Works fine.

@Mail Webmail

Uses the namespace returned via Dovecot, full support via IMAP/POP3 using @Mail. Can also read mailbox quota via the getquotaroot IMAP command.

RainLoop Webmail

Works fine.