The following non-delivery report:
The recipient won't be able to receive this message because it's too large
means that the message size exceeded the limit set on the recipient side.
The Diagnostic information for administrators section also contains the following error:
#550 5.2.3 RESOLVER.RST.RecipSizeLimit; message too large for this recipient ##
By default, in Smarsh Hosted Services environment the outgoing and incoming message size limit for Exchange mailboxes is 50Mb. The limits can be changed under Services > Exchange Mailboxes > username > Advanced Settings > Limits:
The information about the message size limit is also shown in the bounce back message itself:
To resolve this issue:
- decrease the message size
- contact the recipient to increase the message size limits (for messages less than 50Mb)
Note: due to message encoding that is used to transfer the message through the Internet, the size of the message can grow substantially. The encoded message size is the size of the resulting email message with all of the attachments added and encoded using MIME. This encoded size is the actual size of the message as it travels over the Internet and is always larger than the raw size because of the MIME overhead and because binary attachments are generally encoded using base64 encoding. Base64-encoded files are usually about 137% the size of the original files. Additionally, the encoded message contains all of the metadata about the message — and this information grows as the message travels from the sender to the recipient.