We have one distribution group out of 900ish that will not receive mail externally.
In SMG it gets Drop invalid recipients, All recipients are invalid.
Every user in the distribution group is valid, it does not make it to our EX2010 servers. The email address has a & in the middle of it, if I create an alias in the distribution group (converting the & to and) and email it comes through fine.
Does SMG have issues with certain ascii characters? Has anyone expierenced this beforw?