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Maximum E-Mail Message Size

Overview   |   Max E-mail Size   |   Max File Size   |   Corrective Action



All e-mail systems, public, private, commercial or otherwise, have a maximum message size that they are willing to handle. The maximum message size helps to prevent abuse. This page describes how the maximum e-mail message size works.


Maximum E-mail Message Size

The maximum message size for the Santa Clara County ARES/RACES e-mail service is 10 MB (10,240,000 bytes). This includes the message headers, message body, and any attachments.

This size is large enough to handle large attachments, such as images, spreadsheets, PDFs, presentations, and other documents. It also helps to ensure that very large files are not sent over the shared RF access channels.


Maximum Attachment File Size

The file size shown in the PC's file browser may NOT be the same as the file size that the mail server sees. This is because binary files must be encoded so that they can travel throught the 7-bit Internet e-mail infrastructure. The encoding can add as much as 40% to the file size. Therefore, when sending binary files as attachments to an e-mail, the maximum file size as shown in the PC's file browser is actually about 7.2 MB. The file size conversion, due to encoding, can be summarized as follows:.

(File size shown in file browser) X 1.4 = approximate e-mail attachment size

Also, remember that the total message size includes the attachment size plus the size of the email itself (headers, message body, etc.).


Non-Delivery Notification:  message size exceeds size limit

People who try to send a message that is larger than the maximum e-mail message size to the ARES/RACES account will receive a Delivery Status Notification (DSN, also commonly called a "bounce message") from their sending e-mail system indicating that the message was rejected. The exact format of the DSN may vary somewhat. But it usually looks something like the following.

This example resulted from trying to send a 8.033 MB Zip file as an e-mail attachment.

From: MAILER-DAEMON (Mail Delivery System)                    
Subject: Undelivered Mail Returned to Sender

This is the mail system at host <sender's mail system hostname>.


               The mail system
<your-email-address>: message size 11258965 exceeds size limit 10240000
of server[]


Corrective Action


If you have E-mail Networking Information that you would like to have included here,
please contact the Webmaster, Phil Henderson

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This page was last updated 13-Jan-2017