Hi, I am seeing the following log lines on some accounts on my setup:

Sep 11 01:42:36 xxxx dovecot: Panic: IMAP(xxxxxxxxxxxxxxxx): file index-sort-string.c: line 610 (index_sort_add_ids_range): assertion failed: (skip > 0) Sep 11 01:42:36 xxxx dovecot: IMAP(xxxxxxxxxxxxxx): Raw backtrace: imap [0x5555555d3690] -> imap [0x5555555d36f7] -> imap [0x5555555d2d58] -> imap(index_sort_list_finish_string+0xf13) [0x5555555a04b3] -> imap(index_storage_search_next_nonblock+0x432) [0x55555559cd22] -> imap(mailbox_search_next+0x21) [0x5555555a42b1] -> imap(imap_sort+0xdc) [0x555555577ddc] -> imap(cmd_sort+0x33d) [0x555555570ead] -> imap(cmd_uid+0x54) [0x555555571934] -> imap [0x55555557234c] -> imap [0x555555572402] -> imap [0x555555572c1f] -> imap(client_input+0x62) [0x555555572e42] -> imap(io_loop_handler_run+0xf8) [0x5555555da6d8] -> imap(io_loop_run+0x1d) [0x5555555d972d] -> imap(main+0x462) [0x55555557a5f2] -> /lib64/libc.so.6(__libc_start_main+0xf4) [0x2b7c871d8154] -> imap [0x55555556c8c9]

these assertions happen when ordering by from and go away by deleting index files.

As usual if you wish I can send you the index files as they were when this error happened.

Thanks,

Nuno Lopes