** I agree to the code of conduct and the contributory guidelines **
Tested with 80+GB single inbox via imap
``` --nofoldersizes --skipsize --fast ``` file and folder sizes are only used for statistics, which are completely useless. Before the actual data is transfered the message and folder sizes need to be calculated on a 200 000+ message inbox, this will almost never complete.
``` --buffersize 8192000 ``` sets the io buffer to 8mb, the default buffer is 4kbyte, this is speeds up syncs.
``` --skipheader 'X-*' ``` X headers vary wildly from system to system and do not ensure message uniqueness, they are not needed.
``` --split1 3000 --split2 3000 ``` split the requests in several parts on the server, 3000 is the number of messages handled per request.
``` --fastio1 --fastio2 ``` use fastio
Where there is a lot of folders in a mailbox the output may be larger
than TEXT will allow (64KiB). Instead use MEDIUMTEXT (16MiB) which
should be ample.
Additionally check that a sync isn't already running before starting
a new one.
Fixes: #1011
