Starting in version 3.8 on iOS, users can now send emails directly into Day One. Each journal has an individual email address to which users can send emails for creating entries. Since Sync is necessary for this feature, a Premium subscription is required.
In Day One iOS, go to Settings > Journal > tap any journal. The journal email is below the encryption and On This Day settings. Tap the email to pull up a contextual menu of options like saving the email address in your contacts. Then send an email to that address and a Day One entry will be created.
Attachments are not currently supported. Email entries does work with encrypted journals.
When you save a journal email to your Contacts app, an image is automatically placed in the contact with the Day One logo and the color matching the specific journal color.
Emailing an entry does support the same Markdown options we currently support.