Sometimes users get error messages such as "Attachment failed" due to proxy or firewall, when they are trying to upload attachment in Gmail and they start searching for the solution to fix the issue of Gmail attachment failed issue. Here I am also providing some steps to resolve the issue of attachment failure in Gmail. 

1. Open Gmail in other browser,

2. Update the browser,

3. Check your Basic (internet connectivity)

4. Disable all extensions

5. Clear cache and Data

6. Check your attachment size limit

7. Try Gmail mobile app

That’s it. You need to follow all these steps properly to resolve issues related to Gmail attachment.

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