550 your message does not conform to RFC2822 standard
This error is often encountered when using Earthlink as an ISP but can occur with other ISPs?
standard specifies that only one email address can be in the 'to:' email field. However it has become standard practice to allow more than one email address in this field. If your ISP adheres strictly to the RFC2822
standard you may receive this error from several programs including BackupAssist
To rectify the situation go to the Notifications tab of your job, click on 'Setup email addresses' and make sure that there is only one email address (at most) in each of the 'Send tape change reminder emails to the following people:' field, the 'Send report emails to the following people:' field and the 'Send maintainence reminder emails to the following people:' field.
The 'Also CC report emails of backup failures or errors to the following people:' field is unaffected and can contain any number of email addresses.