>>the server rejected the sender address. the server response was 550 access denied invalid helo name

I ran into something similar recently. The From address was coming from a table field and hadn't changed,
but the client changed the domain name of its web site, making my old one invalid.
I'm not sure the message was exactly what you're getting but it said that the sender address was invalid.
I put in the new domain name into the sender address and all was OK