Can anyone shed any light on the error message below when we send from a Google Apps account to any iHug or address? There is an attachment on the message (monthly invoice) but it is less than 100k in size.

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain by [].

The error that the other server returned was:
421 Exceeded allowable connection time, disconnecting.