You can make a Placeholder Gallery to "hold the spot" of a gallery before you upload photos and publish the actual gallery, allowing you to collect email addresses of visitors who wish to be notified of the gallery's availability.
When to use a placeholder gallery
Perhaps you're a wedding photographer. At the wedding reception, you could have cards on display with your same-day slideshow that says:
"To view Mary and Joe's photos, visit bryan.client.photos/galleries/mary-joe"
You could also have the bride and groom share this link on their wedding website and on social media.
This link would be a placeholder gallery that you previously published since you obviously won't have the photos ready for a few weeks. Once the guest visits the placeholder gallery, they'll be asked to enter their email address so they can be notified once the gallery is available.
Then, in a couple weeks, once the gallery is made available, you publish it and take it out of placeholder mode, email the guests who signed up to view it, and they can all go and view the photos.
How to make a placeholder gallery
There are two ways to make a placeholder gallery:
When first creating a gallery, enable the "Placeholder" toggle in the "Add Gallery" modal.
Once a gallery is created, enable the "Placeholder" toggle in the "Settings" panel.
When you publish a gallery in placeholder mode, it will not be available for viewing photos, but instead, will be an email collection form.
Note: You can still upload photos, create collections and set a featured image, but only the cover photo will be viewable until the gallery is no longer a placeholder gallery.
How to see who's signed up to be notified about a gallery
When a gallery is in placeholder mode, you can view who has signed up to be notified of the gallery's availability. Go to the Edit Gallery page, and you'll see the "X Guests" button next to the "Placeholder" toggle, which indicates that the gallery has X number of guests signed up to view the gallery.
Click the "X Guests" button to view more details.
How to manually add guests to the guest list for a placeholder gallery
While in the "Guests" modal (click the "X Guests" button while editing a gallery), you can manually add guests/emails to the guest list for the placeholder gallery.
How to take a gallery out of placeholder mode
To take a gallery out of placeholder mode, and therefore make the photos available for viewing, simply disable the "Placeholder" toggle in the "Settings" panel while editing a gallery and click "Update" or "Save".
How to email all guests who signed up to be notified of a gallery
Once the gallery is out of placeholder mode, you can send an email to all guests who signed up to be notified of the gallery's availability. Click the "X Guests" button while editing a gallery, and then click the "Send Email" button.
This will open up the "Compose Email" modal with all the "To" emails automatically populated, where you can type your email to the guests to let them know that the gallery is available for viewing.
Note: You can also export the list of emails to a CSV for importing into any other online marketing platforms.