E-mail not being delivered

A friend of mine has been sending me e-mail but it gets returned to them with the following message:One or more mandatory argument(s) were missing from the recipient
The MTS-ID of the original message is: c=US;a= ;p=Susquehanna Heal;l=NTMAIL3-060925212552Z-353940

There were no problems before and no changes were made on my end
No problem with other peoples e-mail
They are on a business network

Anyone have any idea what this may be whether my end or theirs

Thnx
eyeblazin

 

is this an exchange server and if so what version

 

she is on a hospital network where she works so I'm not sure. When she sends to my work e-mail I have no problem. I have several comps at home if I check e-mail on other comp I do get them so must be a setting on new comp either blocking them although I was getting e-mail before and it just started blocking hers. I haven't taken time to go through and compare settings on the two machines yet