Dropbox for Gmail

If you use Dropbox for storing important files and if you frequently have to attach files from your Dropbox account when sending Gmail messages, you can check out Dropbox for Gmail.
This is a Google Chrome extension that adds a Dropbox button to your "Compose New Message" window, right next to the "Send" button on the bottom side. It gives you the possibility to send files straight from your Dropbox account, thus excluding the need to manually download Dropbox files just to be able to forward them to someone.

Send files straight from your Dropbox account when using Gmail

The nifty tool is a great time saver when your work implies sending many emails with various files on a daily basis. Easy to use, the extension can be quickly downloaded from the Chrome Web Store and integrated with your browser. Make sure to log in with a Google account to sync data across all devices.
As far as privacy is concerned, the extension asks for permission to read and change all your data on the websites you visit, show notifications, read and edit data you copy and paste, as well as communicate with cooperating native apps.

Select Dropbox files to attach, without leaving the Gmail window

Next, you can visit your Gmail account associated with your Chrome account and try composing a new message. Next to the "Send"  button is the easily recognizable Dropbox icon. After authentication, you can effortlessly explore your Dropbox folders and files without leaving the Gmail window.
One or more files can be selected to attach them to the current email. Furthermore, you can check out a list of recently attached files, swiftly find a file if you're unaware of its whereabouts, and even upload files from your computer to your Dropbox account to keep it up to date.

Sends public Dropbox shared links for download, not file attachments

Attached photos can be previewed in the email. Even so, photos (and any other types of files) are represented by direct Dropbox download links, as long as they're made public in your account.
Therefore, Dropbox for Gmail is different from typical file attachments because it doesn't actually attach files but direct download links to your Dropbox account. The biggest advantage is that it skips the file size limit restricted by Google.