I don't have any way of fixing it, as it is google's doing, not mine. I do see that your messages have been caught in the pending messages list, and I've been releasing them when they are there, unless there are several that are the same (from multiple tries on your part).
Google seems to be more aggressive lately about flagging things that it things are spam. One thing you might try is to delete the quoted material from the previous messages rather than leaving it at the bottom. It might reduce the material that Google thinks is problematic.