What Is Stripping Attachments Out of Gmail?by Josh Fredman
If you get an email that should have attachments but doesn't, they aren't simply lost. Something deliberately removed them along the way. Google doesn't generally strip attachments from incoming emails, though it will do so in specific instances for security and bandwidth reasons. However, in many cases the problem doesn't come from Gmail itself but rather from issues on the sender's end or from interference in the middle.
Gmail for Google Apps
Gmail for Google Apps offers additional productivity tools beyond those available to stand-alone Gmail users, including the ability to remove some or all attachments from both outgoing and incoming email. If you or the message sender uses Gmail for Google Apps, check with the system administrator to see whether the account currently has attachment removal enabled. If you or the sender has administrative access to the Google Apps administrative controls, you can implement a fix to the attachments settings. Sign into the Google Admin console and select "Gmail." Then click on the "General" tab and scroll down to the "Organizations" section, and make the necessary changes to the Attachment Compliance options. You can be very specific with your customization, still removing attachments in general but permitting them in special cases.
Outlook and TNEF Formatting
Microsoft Outlook is one of the few email services that offers TNEF email encoding, a proprietary Microsoft method for packaging emails. If the sender uses TNEF encoding in Outlook, many other email services -- including Gmail -- might not be able to access any attachments that come with the message. If you aren't sure whether this is the cause of the problem, search the email for an attachment that reads "winmail.dat," which indicates that TNEF encoding is to blame. To work around this, have the sender disable or bypass TNEF encoding. The easy fix is to have the sender use a different email service, or use Outlook but choose to send the email in plain text or HTML format rather than RTF format. If that doesn't work, download and install a third-party TNEF decoder like Winmail Opener, Winmail.dat Reader or Free File Viewer on your own machine.
Google doesn't generally strip attachments from incoming emails, but other email services might. If you receive a message that should have attachments but doesn't, check to see whether it came directly from the sender or instead passed through one or more forwarding accounts. If so, have the sender transmit the email to you directly.
Prohibited File Types and Sizes
Gmail doesn't permit you to send or receive certain file types, particularly executable files or corrupted files. As of 2013 it also doesn't enable you to send or receive attachments above 25MB in size. To get around the file type prohibition just have the sender manually change the file extension to an acceptable one, like JPG. When you receive the file, simply change it back to the original extension. To get around the file size prohibition, have the sender use a file compression utility like 7-Zip or WinRAR to split the file into two or more parts and email them individually.