I started exploring this issue when I was having difficulty attaching a zip file to an email in GMAIL.  At first I thought there was a file within the zip that was keeping it from uploading to GMAIL.  After double checking the list of unacceptable formats on google's info page here https://support.google.com/mail/answer/6590?hl=en  I know there isn't a file that would keep it from attaching to the email.

I doubled checked this by creating another zip, with Ark, with just a text file in it.  Same issue, blocked by Google.

Thinking it was a problem with how the zip file was created with Ark, I decided to use another program called "zip" through a terminal.  I created the file, tried attaching it to a gmail message, and it works.

I also checked the bad zip file created with Ark with the "-F" option, using the "zip" program through the terminal, and this is the output I get 

Fix archive (-F) - assume mostly intact archive
        zip warning: bad archive - missing end signature
        zip warning: (If downloaded, was binary mode used?  If not, the
        zip warning:  archive may be scrambled and not recoverable)
        zip warning: Can't use -F to fix (try -FF)

This leads me to believe that Ark is making bad zip files.  I am still able to unzip the files with Ark or other applications, but something is not quite right enough with the arhive to keep google from allowing them attached to an email.

.tar.gz arhives made by Ark work just fine with gmail, which leads me to believe that the problem is specific to .zip arhives

Reproducible: Always

Steps to Reproduce:
1.Select file in Dolphin
2.Right click on the file
3. click on Compress>As Zip Archive>
4. Attach created archive to gmail message

Actual Results:  
Gmail throws a blocked message that says

"Blocked for security reasons! Help"

Expected Results:  
No message, just attaches like any other file would.

I am running Kubuntu 14.10

Dolphin Version 4.14.1 (file browser)

I am using Google Chrome Version 41.0.2272.76 (64-bit)