Does modusCloud limit attachment sizes?

Standard Messaging:

ProofPoint Essentials supports email attachments up to 100MB in size by default - however, many organisations' mail servers enforce a lower size restriction on attachments than this (sometimes as low as 10MB). 

If you are having problems sending emails with large attachments, this is most likely due to a restriction on the recipient's mail server. If you are having problems receiving email with large attachments, please consult your organisation's Tech Contact.

It is also possible to create filters to impose size restrictions on inbound and outbound emails at both an Organisation and User level in ProofPoint Essentials. 

Encryption Messaging:

ProofPoint Essentials encryption service does not use the same messaging gateway. The maximum file size when using encryption services is 35MB.