Email rejected due to large size RRS feed

  • Question

  • Hi,

    I have MS Exchange 2016 and I sent an email with 4 attachment with 3MB size of each file(Total 12 MB). But email bounced back with error "The maximum message size that's allowed is 15 MB. This message is 16 MB." I just want to know how size reached to 16MB while I sent email with 12 MB attachments and with Text "Test" only.



    Monday, September 24, 2018 12:16 PM

All replies

  • This is expected , there is normally an increase of 30-40 % in size due to MIME conversion when sending through Exchange/SMTP.

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    • Proposed as answer by Troy Werelius Monday, September 24, 2018 3:09 PM
    Monday, September 24, 2018 12:43 PM
  • Fazal is correct

    When  an email message with or without attachments is sent to another host via SMTP, the message size may change due to the encoding used to package the message.

    Even if an attachment is less than the set messaging limits, the attachment may not be accepted because its MIME-encoded or UU-encoded size is too large.

    An incoming MIME-encoded e-mail with attachments can increase in size anywhere from 30 percent to 40 percent, depending on how many separate attachments, line breaks, MIME headers or other non-data elements are in the message.

    The exact size can vary enormously, especially since mail systems all behave a little differently when converting e-mail and attachments to MIME. The same problem exists in reverse, where messages sent from your domain will be constrained by message limit sizes on other hosts. Likewise, mail sent from your domain is going to expand anywhere from 30% to 40% in size when converted.

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    Monday, September 24, 2018 3:09 PM