felixroeser/mail — comment on commit 219717c453d1b275ab6235cb1909e49eaabba409
File:  line 0
By sandal:

We've been hitting this problem in github.com/sandal/newman. I have not tested this fix, but it looks like what I would have done. If you look back at the Mail 2.3.0 source which ONLY does a select(), it seems to indicate that these are inverted, for sure.