Mail queue errors

We regularly get errors in our mail queue within the SMC. Some are legitimate and easily fixed, but there are a couple of errors that consistently recur.

"Unexpected end of file while parsing Name has occurred. Line 7, position 1109."

With this one, the message body tag is not closed properly for some reason: eg, it ends liek this:

</initials><s

The other one we see a lot is:

"Service not available, closing transmission channel. The server response was: 4.4.1 Connection timed out"

What are the root causes of these errors? Are they bugs?

Regards,

Mat