Email attachment size limits

Situation – You are having trouble sending/receiving emails with large attachments and wondering if Spambrella enforces a limit on attachment sizes.

Solution – This article provides information on the attachment size limit imposed by Spambrella and what to expect if that limit is exceeded.

  • Standard Messaging – 150MB Limitation
  • Encrypted Messaging – 35MB Limitation


Due to encoding, email programs can add up to 1/3 of the original attachment size to the message. Please keep this in mind when adding attachments.

Standard Messaging

Spambrella supports email attachments up to 150MB in size by default – however, many organizations’ 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 an email with large attachments, please consult your organization’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 Spambrella. For more information on this process, please see our Knowledgebase entry on filter creation.

Encrypted Messaging

Spambrella’s encryption service does not use the same messaging gateway. We rely on Proofpoint to provide technologies which include: PKI, S/MIME, X.509 certificates, 3DES, AES-256, and 1024- bit RSA keys (with MDS and SHA-1 encryption algorithms).

The encrypted message web portal utilizes a 128-bit secure sockets layer (SSL). The maximum file size when using Spambrella encryption services is 35MB.

Total Email Size Versus Attachment Size

  • Attachments sizes can be seen on a computer when you view their properties.
  • Total Email Size is not the same size. Emails require the attachment to be encoded as part of the body. This encoding process will increase the size of the email up to 33% in most cases.

For the total size to be 35MB, the actual attachment should not exceed 23MB. This is the safest amount when using Encryption.

What Happens To An Email That Exceeds The Limit

  • Standard – When a Standard email attachment exceeds the size limit, it will be hard bounced.
  • Encrypted – When an Encrypted email attachment exceeds the size limit, it will be stuck in a queued state in the email message logs and will fail to be uploaded to the Encryption Portal.

Administrator Topics

What is the Email Management Platform?

SPF Checking with Office 365