See http://kb.mozillazine.org/Moving_your_mail_storage_location_-_Thunderbird

<blockquote>if the image is 10 MB, will there then be 10MB less left of the C drive’s total storage space?</blockquote> It does actually take more, but you don't have to guess, you may make Thunderbird show how much space each message takes by using <b>Table View</b> (you must be using <b>Cards View</b> if you're asking this question), and add the <b>Size</b> column if not already shown: https://support.mozilla.org/kb/getting-started-thunderbird-main-window-supernova <blockquote>is there any way to move the whole Thunderbird (emails with images) over to the D drive</blockquote> I'd move the whole profile folder and keep it all together rather than the local directory of each of the accounts, for which I provide instructions below, BUT… before you do any of that… Are you sure you want to keep all those images in your mail? Wouldn't it be preferable to save them, organise them separately however you wish, and remove them from the messages they came with? Anyway, to move the profile folder to a new location on drive D… Check the following article to see what's a profile and how to locate the profile folder, but don't follow the instructions given there to move the profile unless you feel comfortable manually editing the <i>profiles.ini</i> file as described there: https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data Do this instead: # In Thunderbird, choose <b>File > Offline > Work Offline</b> from the menu bar, so Thunderbird doesn't connect to the server while you're doing this. # Locate the profile folder you want to move to another drive. # Quit Thunderbird. # <b>Copy</b> (don't remove from the original location yet) the profile folder to the desired new location. # Launch Thunderbird, choose <b>Help > Troubleshooting Information</b> from the menu bar and click on the <b>about:profiles</b> link there to open the <b>About Profiles</b> built-in Profile Manager. # <b>Create a New Profile</b>, read the introductory text if this is new to you, then click <b>Continue</b>. You may name the profile however you want, but I'd choose a name such as "D-Drive" that makes it clear this is a profile stored outside of the default location. # Click <b>Choose Folder</b> to choose the profile folder in the new location, then click <b>Done</b>. # Click <b>Launch Profile</b> under the new profile in the profile manager to start using the new profile. Don't go online yet, make sure first that everything is working as expected. In particular, you may check the <b>Server Settings > Location Directory</b> of your mail accounts to see that your mail is now being stored where you expect. # Go back to the profile manager. The new profile may have already been set as the default. If not, use the <b>Set as default</b> button under it to make it so. # <b>Remove</b> the old profile. You'll be given the option to <b>Delete Files</b>, which is the very reason we're doing this. # Tell thunderbird to go back online by unchecking <b>File > Offline > Work Offline</b>. You may see similar instructions to accomplish the same using an external Profile Manager tool. That additional complication is unnecessary. Recent versions of Thunderbird have the built-in version of the Profile Manager I've been referring to that may be used instead. Both versions of the Profile Manager are documented in the following article: https://support.mozilla.org/kb/profile-manager-create-and-remove-thunderbird-profiles