MailStation problem (IMAP) mit grosser Mailbox

[c0r0n3r]

Hallo,
ich habe eine Mailbox die ich zu Backup zwecken nutze - diese hat einige tausend eMails gespeichert.

Seit einigen Wochen kann ich per IMAP keine Listung mehr abrufen, nach langer Suche bin ich auf die folgenden Logfiles aus 'doveadm log errors' gestossen:

Dec 05 20:38:18 imap(mailuser): Warning: Maildir: Scanning /var/services/homes/mailuser/.Maildir/new took 87 seconds (1 readdir()s, 1 rename()s to cur/, why=0xc0)
Dec 05 20:38:52 imap(mailuser): Fatal: block_alloc(16777216): Out of memory
Dec 05 20:38:52 imap(mailuser): Error: Raw backtrace: /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(+0x7e220) [0x7f8e876b6220] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(+0x7e30c) [0x7f8e876b630c] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(i_error+0) [0x7f8e87661227] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(+0x95e44) [0x7f8e876cde44] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(+0x95e83) [0x7f8e876cde83] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(p_strdup+0x28) [0x7f8e876dbfa8] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(maildir_uidlist_sync_next_uid+0xed) [0x7f8e879a1b8d] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(maildir_uidlist_sync_next+0x12) [0x7f8e879a1f92] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(+0x6b77f) [0x7f8e8799f77f] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(+0x6c4f4) [0x7f8e879a04f4] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(+0x6c7d2) [0x7f8e879a07d2] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(maildir_storage_sync_init+0x91) [0x7f8e879a0ab1] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(mailbox_sync_init+0x2b) [0x7f8e87976feb] -> /var/packages/MailServer/target/lib/dovecot/libdovecot-storage.so.0(mailbox_sync+0x27) [0x7f8e879770f7] -> dovecot/imap(cmd_select_full+0x168) [0x413f78] -> dovecot/imap(command_exec+0x75) [0x41a7b5] -> dovecot/imap() [0x418c02] -> dovecot/imap() [0x418c90] -> dovecot/imap(client_handle_input+0x11d) [0x418fdd] -> dovecot/imap(client_input+0x75) [0x419395] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(io_loop_call_io+0x4c) [0x7f8e876c8fac] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(io_loop_handler_run_internal+0x110) [0x7f8e876c9b70] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(io_loop_handler_run+0x25) [0x7f8e876c9035] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(io_loop_run+0x38) [0x7f8e876c91d8] -> /var/packages/MailServer/target/lib/dovecot/libdovecot.so.0(master_service_run+0x13) [0x7f8e87666793] -> dovecot/imap(main+0x2d7) [0x40ce77] -> /lib/libc.so.6(__libc_start_main+0xf0) [0x7f8e872b3030] -> dovecot/imap() [0x40d002]
Dec 05 20:38:53 imap(mailuser): Fatal: master: service(imap): child 29776 returned error 83 (Out of memory (service imap { vsz_limit=256 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)

Ich habe versucht folgende Konfigurationsfiles anzupassen:
./etc/template/dovecot.template - mail_process_limit auf 0
./etc/template/dovecot.template - service imap { vsz_limit =0 } hinzugefügt
./etc/dovecot/conf.d/20-managesieve.conf - vsz_limit = 64M auf vsz_limit = 0 geändert
./etc/dovecot/conf.d/10-master.conf - imap-login process_limit auf 0 gesetzt

Leider hat all das nicht geholfen...

Modell: DS1512+
DSM Version: DSM 6.2.1-23824 Update 1

Hat jemand hier Erfahrung bzw. weiss jemand wo ich die RAM Einstellung für den IMAP Service ändern könnte?

Vielen Dank für jegliche Hilfe!