SMART CATALOG Mail Sending function uses that of the device's. For example, on an iOS device, it is possible to send files of up to 25MB. However, in case the device's mail sending function limits its available file size as under 25MB, the available file size is affected by the limit.
Meanwhile, the PDF that is sent by e-mail is a PDF that has been uploaded to the CMS and then converted as distribution content. The file size may be bigger than the original one because the converted PDF is optimized for content distribution.