Request:

May 10 16:45:04 sogod [753409]: 2003:a:61b:bb01:11a9:aa81:2d79:19c9 "POST /SOGo/Microsoft-Server-ActiveSync?User=mbozem&DeviceId=NFBK5LNQKL1MV8OU1R2VAB7PI0&DeviceType=iPhone&Cmd=Sync HTTP/1.1" 200 0/65 0.164 - - 0 - 13
May 10 16:45:04 sogod [753409]: <0x0x56239e4a1010[SOGoActiveSyncDispatcher]> EAS - request for device NFBK5LNQKL1MV8OU1R2VAB7PI0: <?xml version="1.0"?>
<!DOCTYPE ActiveSync PUBLIC "-//MICROSOFT//DTD ActiveSync//EN" "http://www.microsoft.com/&quot;>
<Sync xmlns="AirSync:">
<Collections>
<Collection>
<SyncKey>0</SyncKey>
<CollectionId>mail%2Fshared</CollectionId>
<Options>
<FilterType>5</FilterType>
<MIMETruncation>1</MIMETruncation>
<MIMESupport>0</MIMESupport>
<BodyPreference xmlns="AirSyncBase:">
<Type>1</Type>
<TruncationSize>500</TruncationSize>
</BodyPreference>
</Options>
</Collection>
</Collections>
</Sync>

About 5 requests per second until the client is terminated.

Mailserver: dovecot
Version: 2.3.16

Shared folder definition:

namespace {
type = shared
separator = /
prefix = shared/%%u/
location = maildir:%%h/Maildir:INDEX=%h/shared/%%u:CONTROL=%h/shared/%%u
inbox = no
hidden = no
list = children
subscriptions = no
ignore_on_failure = no
}