We have discovered a problem with Xeams that occurs when you use Smart Host in Xeams along with SMTP Proxy server in "Asynchronous" mode. We will fix this in the next update. In the meantime, switch the SMTP Proxy server back to "Synchronous" mode by Unchecking "Asynchronous Mode" in SMTP Proxy Server setting. That will fix the problem.
Apparently, this bug has been there for a long time but it did not appear because you were using SMTP Proxy Server in Synchronous mode. Asynchronous mode is better than Synchronous and the last update switched the default value for this parameter, which made the problem appear.
Let us know if anyone wants a patch before it's released to general public.