When we send out overdue notices to individuals in a different domain, we receive the following error message: Failed to send message to [whatever address] using SMTP: 'There was a problem with the server with the RCPT command.'.
For example, we are able to send messages to everyone with an email ending @med.va.gov but everyone else at a different domain (i.e. @yahoo.com or @bcm.tmc.edu)gets a failed to send message.

I have looked at the inmagic.ini file and it is set to the following:

Use SMTP: 1
SMTP ServerName:
SMTPIPAddress1:##
SMTPIPAddress2:###
SMTPIPAddress3:##
SMTPIPAddress4:###

Thanks