BAD maximum literal size exceeded

I'm migration from ZCS 6.0.6 to 8.0.1_GA_5438.FOSS with imapsync-1.350-1

I use the following line;
imapsync --nofoldersizes --skipsize --fast --buffersize 18192000 --nosyncacls --exclude 'Trash|Emailed Contacts|Contacts' --syncinternaldates --noauthmd5 --host1 $host1 --user1 $user --password1 $pass --host2 $host2 --port2 7143 --delete2 --user2 $user --password2 $pass

Everything works just fine but some emails doesn't sync with the following errors;
BAD maximum literal size exceeded

Those emails all have attachments but they are variable in size, from 126Kb to 7Mb.

Anyone knows what exactly what "literal size" means? Or have any clue how fix/prevent this?

Thanks!

Steeve