OS X Cryptomator and Email software Postbox

I am using Cryptomator for normal directories and it works fine on Mac OS X.
But with the emai software Postbox I have the problem, that Postbox can sometimes not write emails e.g. to the sent folder.
Postbox support cannot support this.
They say, maybe the files are locked.
Without Cryptomator it works fine, e.g. with VeryCrypt. But with VeryCrypt I have a sync problem with the container.
Can someone help with email programs and Cryptomator?