Message Not Delivered: Too many recipients for message
The message could not be delivered because it was addressed to more recipients than the email systems involved could handle.
Fixes
Divide the list ofrecipients into two groups and send The email message each group separately.
If this problem still occurs, divide your list further, e.g. into four, six, or more groups.
5.5.3: Official Definition
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 5.X.X:
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.
[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.5.3:
More recipients were specified for the message than could have been delivered by the protocol. This error should normally result in the segmentation of the message into two, the remainder of the recipients to be delivered on a subsequent delivery attempt. It is included in this list in the event that such segmentation is not possible.