This is still going on - we just had 20 workers consuming 2.5GB each. It seems to be due to an initial ActiveSync from a user who had an empty inbox on opening Outlook.

Show your complete sogo.conf file.

You should NOT set SxVMemLimit to a high value if you have many workers.

What you see is the "normal" memory usage behaviour with autorelease pools in GNUstep.

{
OCSFolderInfoURL = "mysql://xxx:xxx@server:3306/sogo/sogo_folder_info";
SOGoProfileURL = "mysql://xxx:xxx@server:3306/sogo/sogo_user_profile";
OCSSessionsFolderURL = "mysql://xxx:xxx@server:3306/sogo/sogo_sessions_folder";

SOGoMaximumPingInterval = 10;
SOGoInternalSyncInterval = 10;

SOGoEnablePublicAccess = YES;

SOGoEnableEMailAlarms = YES;
OCSEMailAlarmsFolderURL = "mysql://xxx:xxx@server:3306/sogo/sogo_alarms_folder";

SOGoMailAuxiliaryUserAccountsEnabled = YES;

SOGoMaximumSyncWindowSize = 10;

SOGoSieveServer = "sieve://server:4190/?tls=YES";

SOGoMailingMechanism = smtp;
SOGoSMTPServer = server;

WOPort = "server2:20000";

SOGoIMAPServer = "imaps://server/?tls=YES";

SOGoMailDomain = domain.no;

SOGoMailMessageCheck = every_minute;

SOGoSMTPAuthenticationType = PLAIN;

SOGoForceExternalLoginWithEmail = YES;

SOGoUserSources = (
{
type = ldap;
CNFieldName = cn;
IDFieldName = cn;
UIDFieldName = userPrincipalName;

IMAPHostFieldName = mailHost;

baseDN = "CN=Users,DC=domain,DC=no";
bindDN = "CN=xxx,CN=Users,DC=domain,DC=no";
bindFields = (sAMAccountName,userPrincipalName);

MailFieldNames = (userPrincipalName);

bindPassword = xxx;
canAuthenticate = YES;
displayName = "Active Directory";
hostname = terminalserver.domain.no;
id = directory;
isAddressBook = YES;
port = 389;
mapping = {
mail = userPrincipalName;
};
}
);
SOGoVacationEnabled = YES;
SOGoForwardEnabled = YES;
SOGoSieveScriptsEnabled = YES;
SOGoMailUseOutlookStyleReplies = YES;
SOGoFirstDayOfWeek = 1;
SOGoLanguage = NorwegianBokmal;
SOGoTimeZone = Europe/Oslo;
SxVMemLimit = 8192;
SOGoMemcachedHost = 127.0.0.1;
SOGoDebugRequests = YES;
SOGoMaximumSyncResponseSize = 10240;
WOWorkersCount = 20;
WOWatchDogRequestTimeout = 120;
}

So how then can we make sure the initial sync works ?

If SxVMemLimit is set too low, the thread exits before the initial sync is done, and no mail is found by Outlook 2013.

That's not true.

SxVMemLimit is looked by the SOGo process AFTER the response was delivered. If the current memory usage of the process exceeds SxVMemLimit, it'll terminate itself and the parent process would spawn a new child.

In any case, the response WAS SENT before this.

Ok, so we can set SxVMemLimit to 1GB, the response will be delivered however large it is - and the process will restart afterwards ?
Is this only for initial sync, or for all requests ?
What are the implications of setting SxVMemLimit too low ?

To answer your questions:

Yes
For all requests
Process will restart too often

Ok, thanks, will lower it now and see how it goes.