Same thing, 554 message refused.
I suspect, it has to do with some sort spam filter at their end. But there should be a way to take care of it. I'm providing user id /password which per logs is getting authenticated successfully, then why are they refusing the email, is beyond understanding. Probably they need some sort of setting, but if their support is not helpful in providing that! ugh!!!
Any other ideas or suggestion?
But regardless, thank you so much for this forum and all the support you (and your team and others) provide here. Thanks!